The Monster Association Arc is the fifteenth arc of the series, and the sixth arc of the Human Monster Saga.
The ninja duo Gale Wind and Hellfire Flame offer Speed-o'-Sound Sonic a monster cell and invite him to join them in their conquest to kill Flashy Flash. Sonic accepts their offer, and takes the monster cell wanting to give up his humanity in order to surpass Saitama.
At the Hero Association, the staff are discussing the sudden monster attack and their quick disappearance. Rabbit, Meat Pounder and Ironet are sent to defeat Marshall Gorilla, but Zombieman offers to go instead. Zombieman observes Marshall Gorilla and notices somebody approaching him. Marshall Gorilla meets Armored Gorilla and was shocked to figure out that Armored Gorilla "sided" with the humans. Marshall Gorilla attacks him with his knife, only for it to break on Armored Gorilla, who proceeds to defeat him in one blow. Watching this altercation, Zombieman decided to follow Armored Gorilla instead.
At the Hero Association HQ, a staff member bursts into the conference room with a message from the Monster Association. It is revealed that the staff member is the host of a parasitic monster. Gyoro Gyoro asks the executives through the staff member not to attack their living area and wishes to have a co-existing society between monsters and humans. However, this is all just a ploy as Destrochloridium kills one of the executives. Gyoro Gyoro proceeds to reveal their real intent which is a war between the groups with their very best. Superalloy Darkshine arrives in time and effortlessly kills Destrochloridium.
Meanwhile, at the Monster Association HQ, the monsters discuss their plan. Awakened Cockroach is eaten by Orochi for losing to Genos and to assert his authority. Do-S was also at risk of being killed, but is spared for her abilities.
Garou wakes up after being knocked out by Saitama and encounters Death Gatling, but decides to call it a day and goes to get some rest. Meanwhile, King dominates Saitama in a fighting game. Gyoro Gyoro discovers that Gouketsu was killed and believes that the fight will be harder than originally thought.
Genos is fully repaired by Dr. Kuseno, who spent the whole night fixing him. Genos thanks him for his efforts and states he will never lose again, to which Dr. Kuseno tells Genos to be careful and not do anything reckless. The Monster Association leaks the information to the public media about the captured hostage and the announced war between them and the Hero Association, and fear spreads among the public. Metal Knight is discussing with Child Emperor about a proposed plan to destroy the Monster Association hideout by killing all the monsters, including the hostage, but as the idea was rejected by the Hero Association, Metal Knight refused to join the mission, much to Child Emperor's annoyance. As the news spread, many monsters decide to join the Monster Association and head towards their hideout, only to be killed by Saitama, who was late for the garbage truck.
Tareo and his friends are discussing about how someone has been using their secret hut in a park. When they arrive, Tareo is bullied into entering the hut to tell the person to leave. As Tareo enters the hut, much to his surprise, he encounters Garou. Outside, Death Gatling has formed a team of A and B-Class heroes to ambush Garou and asks the children to leave. Garou then senses killing intent and concludes he is surrounded and asks Tareo for the Hero Association Catalog to identify the heroes outside his shack.
After identifying all of the heroes, Garou exits the shack. Gun Gun quickly opens fire on Garou, but Garou easily dodges and attempts to counterattack. However, he is forced to dodge again because of Stinger's attack. Stinger's attack is quickly followed up with Arrow Rain from Shooter, which Garou also manages to dodge. Chain'n'toad begins the next wave of attacks as Smile Man attacks from above and Wild Horn attacks from behind. Garou notices Glasses' lack of action, but is then hit by Chain'n'toad's weapon and attacked by Smile Man again. Chain'n'toad uses his Ear Cutter technique, but fails to injure Garou. Smile Man and Chain'n'toad proceed to continuously barrage Garou before the Human Monster has any time to recover. Arrow Rain comes down as Smile Man, Chain'n'toad, and Gun Gun attack all at once. Despite twisting in the air, Garou is hit by two of the arrows. Glasses resupplies Shooter before Garou tries to go after the hero. Glasses manages to dodge Garou's initial attack and lands a hit on Garou as the Hero Hunter is distracted by the heroes behind him. Afterwards, Death Gatling gives Garou one last chance to surrender.
As Garou continues to be attacked by the heroes, he thinks back to a time when the cartoon hero, Justice Man, fought a crab demon and beat the monster with the help of other heroes. Chain'n'toad wraps his chain around Garou's ankle to restrict his movement as Smile Man launches another attack, but Garou redirects the ball to take out Chain'n'toad. Afterwards, he separates the ball from Smile Man's kendama and launches the ball towards Gun Gun, knocking him out. Wild Horn attempts to bring the situation back under control, but just becomes a meat shield for Garou. Glasses and Stinger run to help, but Garou simply uses Glasses' attacks to knock out Shooter. Garou then runs straight toward Stinger as a diversion as he uses roots to disorient the heroes and knock out Smile Man. Death Gatling tries opening fire on Garou, but Garou eventually uses Glasses as a meat shield. Stinger tries to help Glasses, but he and Glasses are quickly taken out by Garou. Death Gatling takes the opportunity to finish off Garou and unleashes a barrage of bullets, but to his surprise, Garou deflects all of the bullets and knocks him out. Unfortunately, before Garou could rest, Genos arrives because of a support request signal sent by Glasses. Garou and Genos begin trading blows. Garou is unable to find an opportunity to counterattack Genos in his current state and resorts to using Watchdog Man's fighting style to confuse Genos.
Meanwhile, King and Saitama continue to play video games. King receives an alert from the Emergency Transmitter. Saitama then leaves, concerned about Genos.
Garou manages to detach Genos' arm, but Genos demonstrates the ability to remotely control his arms and launches Garou towards a tree. Genos then wraps Garou in place and proceeds to use his Incineration Cannons. However, Garou manages to split the tree and fall down. The Monster Association appears to support the Hero Hunter and invites Garou to join their ranks once again, but Garou declines their offer once again.
Before Genos could use his Incineration Cannons on Garou again, Bang kicks Garou. Bang confronts Garou, while Bomb deals with the Monster Association monsters. The former master and student take their respective stances before finally initiating their fight. As Garou is pummeled rapidly by Bang, Garou tries to counter-attack against his former teacher but his efforts are in vain due to his weakened state and their difference in Water Stream Rock Smashing Fist mastery. Knowing that he cannot win, he attempts to escape and uses Death Gatling's unconscious body as a meat shield to cover his escape. However, Bomb intercepts him and kicks him in the face toward the group of remaining monsters, causing the monsters to be shredded by Bomb's razor sharp Whirlwind Iron Cutting Fist.
Bang and Bomb then combine their martial arts against Garou. In a state of great pain, Garou remembers his miserable past as a misunderstood child being bullied. In the his anger and despair, he commences a counterattack by destroying the ground and grabbing a huge tree during the confusion. Garou swings the tree at Bang and Bomb, forcing them to back off. Phoenix Man suddenly appears and rescues Garou while calling for Elder Centipede to cover their escape. While Phoenix Man escorts Garou to the Monster Association HQ, Elder Centipede must fend off the three heroes. Despite their combined strength and even accomplishing significant damage towards Elder Centipede, Bang, Bomb, and Genos were unable to defeat the monster and are forced to retreat. Bang tries to sacrifice himself and unleash his full power to buy Bomb time to escape with Genos and the unconscious heroes. Fortunately, King arrives and catches Elder Centipede's attention by tricking him into believing that he brought Blast with him, making the monster charge toward him. Elder Centipede meets his demise when an unnoticed Saitama, who was behind King, threw a Serious Punch that disintegrated his entire body from head to tail.
The Hero Association staff discuss the recent events. Sitch declares that Garou should be recognized as a Dragon level threat. Some of the staff suggest that Blast should be called, but Stitch explains that the hero acts on his own. Narinki announces his frustration at the Hero Association staff, but Sekingar assures the donator that they will save his son. Sekingar later meets with Superalloy Darkshine, Pig God, Tatsumaki, and Drive Knight about preparations, while Child Emperor works to find the Monster Association HQ. Multiple S-Class heroes and Sweet Mask arrive back at the Hero Association HQ after their investigations. Child Emperor pleads for Bofoi's participation in the assault against the Monster Association, but Bofoi declines once again.
Fubuki attempts to rally Saitama and his acquaintances to take the situation more seriously. However, everyone has an excuse to not accompany Fubuki. Saitama leaves in order to find Garou. Narinki orders Narinki's Private Squad to rescue his son from the Monster Association.
Garou wakes up to find himself inside the Monster Association HQ. Narinki's Private Squad were captured just beforehand by G5 and are left to be judged by Gyoro Gyoro. Do-S then proceeds to make them her love slaves. Afterwards, Garou is requested by Orochi to bring back the head of any hero to prove that he is a mysterious being within one day. Gyoro Gyoro commands Bug God and Royal Ripper to monitor Garou as the Hero Hunter completes this endeavor.
A new group agrees with the monster outbreak and attempts to capture a citizen for disagreeing with their ideology, but have the misfortune of bumping into Garou, who knocks them out with a flick before heading to a nearby restaurant. Saitama is having lunch at the same restaurant, but is not able to pay because he lost his wallet. Coincidentally, Fubuki arrives and begins talking about the Hero Hunter while also once again trying to get him into her hero faction. Saitama misleads Fubuki into eating the fries as Garou dashes out and everyone screams dine and dasher. Saitama then takes the opportunity to go out to "catch" the dine and dasher and push the bill onto Fubuki.
Sometime later, Garou scares some boys who were bullying Tareo. Soon enough Saitama catches up to Garou and lets Garou off with a warning. This severely angers Garou, thinking that heroes are starting to take pity on him. He resolves to carrying out his task by bringing back Saitama's head, but Saitama accidentally punches Garou, knocking him out.
Later, Garou wakes up and asks Tareo who the hero was. Immediately after, Bug God and Royal Ripper confront Garou. Royal Ripper approaches Tareo, to which Garou tells him to back off. Garou assumes a stance in front of Tareo as Bug God and Royal Ripper approach the pair. Royal Ripper reveals that Gyoro Gyoro had sent him and Bug God to follow and monitor Garou. After observing his behavior, they now have doubts about Garou’s intent, questioning whether if he is a true monster or not. Garou then proceeds to provoke Royal Ripper to little use, as the latter then demands the former to kill Tareo. Garou then tells Tareo to go home, but Tareo is unable to do so because of fear. Due to this, Tareo is berated by Garou, who then forces the Hero Association Catalog out of his hand, saying that the boy needs to get stronger during times like these. While doing so, Royal Ripper attacks Tareo. The attack is quickly stopped by Garou, who hoists Royal Ripper up in the air by his blades and swiftly delivers a kick to his opponent’s abdomen. Royal Ripper then flies into the air as a result but is quick to get back on his feet by thrusting his blades onto the ground and performing a somersault with the two blades acting as anchoring points. The move severely disfigured his arms, but Royal Ripper restores his limbs back to their original state by twisting them back. Garou then yells at Tareo, telling him to run. The boy complies and dashes away. As he is doing so, Royal Ripper announces Garou to be an enemy and Garou then assumes a stance as the two monsters charge at him.
At the Monster Association HQ, Gyoro Gyoro is seen meditating on a bean bag while Phoenix Man enters the room. Phoenix Man then asks Gyoro Gyoro for an explanation for sending two aggressive monsters to observe Garou, to which Gyoro Gyoro replies that the two might be able to mentor Garou on killing heroes. Phoenix Man states that the two are too unruly to follow orders and will murder Garou if given the chance. He says that this is especially the case with Royal Ripper, whom even fellow monsters avoid contact with. As a counter-argument, Gyoro Gyoro states that Garou needs to be physically and mentally pushed to the limit to develop and proceeds to explain to Phoenix Man where Orochi came from. Gyoro Gyoro reveals that Orochi was a simple human being, and that he is responsible for the creation of the Monster King and that Orochi only became as such through countless failures and sacrifices on Gyoro Gyoro's part. Gyoro Gyoro then goes on to say that Garou could become the next Orochi if given the same treatment.
Atop a roof, Zombieman is observing a takoyaki shop, suspecting it to be a new front for the House of Evolution. Upon entering the shop, he encounters Armored Gorilla, who assumes Zombieman to be a customer. The hero introduces himself but is surprised by Armored Gorilla after he reveals that the House of Evolution has ceased to exist. Zombieman then meets up with Dr. Genus, who then goes on to mention the fact he fondly remembers Zombieman as the successful immortal specimen that escaped and destroyed his facility. Zombieman then threatens Dr. Genus with a large axe and asks him why the House of Evolution was destroyed, stating that the facility could always be rebuilt as long as Genus is alive. The scientist responds by giving an account of his encounter with Saitama who, according to Genus, had removed his Limiter and possesses greater power than anything artificial. He then expands on the concept of the limiter, explaining that every single being has a limit on how much they can develop because too much power can potentially create mindless rampaging monsters. As such, God created the limiter to restrict everyone’s abilities, thus ensuring their survival and mental integrity. Zombieman then raises the question of whether the person, who removed his limiter, did so without any cost. Genus states that the individual paid for his immense power by losing his hair and having to bear the overwhelming sense of detachment from society. Zombieman responds by saying that those who possess immense powers without becoming a monster are called heroes. Genus then explains that humans become monsters due to internal factors (bad habits, mental abnormalities, or frustration), as well as external (pollutants or chemicals) and, as such are different from those who removed their limiter. Monsters such as the Seafolk appearing in J-City or the Dark Matter Thieves are simply sentient beings that are hostile to humans. As for heroes, Genus states that they already possess potential at birth and managed to develop that potential through extensive efforts. Others could achieve great powers through artificial means such as mechanization, experimentation, or were born with great powers. However, Saitama is an exception, due to the fact that he is an ordinary person with no unique potential whatsoever, but managed to remove the barrier for growth simply through sheer force of will and effort. It is for this reason that Genus relinquished his own ambitions, saying that they are now laughable.
As Royal Ripper and Bug God charge, Garou delivers a punch towards Bug God’s torso. Unfortunately, this injures his own hand. Royal Ripper then performs a chain of frenzied slashes aimed at Garou, but they are all dodged or reflected. As Garou is busy with Royal Ripper’s chain of attacks, Bug God approaches him from behind but is bombarded with a flurry of deflected slashes from Royal Ripper. The monster is undeterred by this as he quickly pounds Garou into the ground and then flings him onto electric cables, which briefly electrocute Garou. Garou immediately rebounds himself towards the two monsters as they leap towards him. The three eventually enter a stalemate, with Garou now confident in his abilities to defeat his opponents, while the pair of monsters declare to go all out. Garou is not discouraged by this, even going on to say that he has seen everything they have to offer and will not be hit by them again. It then transpires that Tareo was captured by Sludge Jellyfish. While Garou is distracted, Royal Ripper and Bug God brutalize him, leaving Garou in a pool of blood. Bug God quickly puts a stop to the assault, explaining that Garou should be left alive. Royal Ripper ceases attacking but declares that it might be too late for Garou. He then invites Tareo back home with an eerie grin, saying that they will be great friends.
In Saitama's apartment, Genos, King, Bang, and Bomb are anxiously waiting for Saitama to return. When Saitama turns up looking dishevelled, they presume that he fought with Garou. Saitama denies it, unaware that he had indeed met Garou and defeated him for the third time. Fubuki also arrives, while Genos detects something approaching fast and sends King to deal with it. The 'monster' is revealed to be Dr. Kuseno, who came in a mechanical suit to check on Genos. Dr. Kuseno introduces himself to Saitama and gifts him high quality meat for hot pot. Saitama instructs Genos to prepare the hot pot before realizing that he would have to share with the other visitors.
Meanwhile, in the Monster Association, Royal Ripper and Bug God try to explain Garou's 'death' to Gyoro Gyoro by putting the blame on Garou and then Gyoro Gyoro. Gyoro Gyoro sees through their antics, but spares them from punishment and tells them to take things seriously as the Hero Association could attack in a few hours. Gyoro Gyoro had captured Child Emperor's scouting robot "Dig Here Woof Woof No. 3".
Many members of the Monster Association are seen preparing, socializing, or otherwise loitering around as they wait for the battle ahead. Tareo, as a prisoner, is put into the same cell as the hostage Waganma. Waganma is confident that his rich status means that the heroes will save him and snobbishly attempts to make Tareo his subordinate. Meanwhile, Garou awakens in the spot where he was abandoned, and begins to move off.
Back at the Hero Association HQ, Child Emperor and Sekingar go through the roster of heroes. Child Emperor becomes paranoid and exerts his influence to remove Demon Cyborg and Silver Fang from the rescue mission. Sitch, despite his protests, is instructed not to inform the two.
At Saitama's apartment, the group of seven are about to eat the steaming hot pot. They rush in with their chopsticks at once, throwing up food into the air. King is instantly knocked out, but nobody notices. Fubuki uses telekinesis to bring a piece of meat toward her, but Genos tries to reclaim it for Saitama, who asks why everyone is eating his food. During the argument that ensues, Dr. Kuseno calms Genos down, only for Fubuki to attempt recruiting the engineer for weapons development. Saitama is annoyed that the meat is already gone, and soon after finds King 'sleeping'.
The Hero Association is about to deploy the S-Class without Watchdog Man, Blast and Metal Knight (With Genos and Bang's whereabouts being unknown to them at the time) to deal with the monsters. Every hero from C-Class to A-Class who is available was sent to deal with the Monster Association's forces, while the S-Class heroes deal with the Dragon-level monsters.
Monster Association RaidEdit
Garou breaks into the facility just in time to save Tareo from Royal Ripper. Despite being stabbed in the gut by the monster, Garou punches Royal Ripper's head off with one blow, killing him in the process, before using Whirlwind Iron Cutting Fist to shred the monster to pieces. Garou and Tareo then make their escape, only to encounter two monsters who were quickly dispatched by Garou. The Hero Hunter devours one of the limbs of the monsters to replenish himself before proceeding with Tareo. As they make their escape, Tareo tells him that there is another child that is in need of rescuing but Garou says that's none of his concern and that he did not come here to save Tareo, either. However, before the two can continue, they are met by Overgrown Rover. Garou and Tareo slowly back away in order to avoid a confrontation. As they are about to turn a corner, Super Mouse suddenly attacks. Garou pulls Tareo back, saving him, while Unihorn and Showerhead follow up by lunging at Garou and dousing him with hot water.
The three monsters launch a united attack on the Hero Hunter, but Garou kicks Unihorn into a wall, cracks Showerhead's faucet, and uses Whirlwind Iron Cutting Fist to cut into Super Mouse's arm. This impresses the monsters and Tareo, to the point where they acknowledge his strength. Tareo claims that Garou is getting stronger, and he states that he's used to fighting multiple opponents. Super Mouse replies that they have been evaluated by Gyoro Gyoro, so their strength is without question, to which Garou responds saying that he should possess a threat level of Dragon. Super Mouse replies again, saying that the threat level Dragon is only reserved for the Monster Association cadres. Super Mouse, Unihorn, and Showerhead reveal that they have been stalling and proceed to attempt to punch a hole through Garou using their Demon Trinity Bursting Speed Thrust. Garou easily deflects the attack back into the hallway, mocking the technique's power. A loud roar is heard down the hallway, prompting Garou to realize that he had deflected the attack into Overgrown Rover. Rover easily dispatches Unihorn and appears before them, firing an energy blast. Showerhead attempts to cancel it out with his maximum water pressure while Super Mouse guards, stating that he can revive himself by regenerating. Garou grabs Tareo and begins to run away. As a result of Rover's blast, everything above ground in Z-City shakes.
Garou manages to break out of the hallway him and Tareo were in, and escape the destruction, but Rover follows them. Garou tosses Tareo to the side, claiming that they have to split up, but Tareo protests. Rover begins charging up another blast, but Garou dashes underneath him and attacks Rover's leg. Showing no signs of being affected at all by Garou's attack, Rover turns and fires a blast directly on top of him. The blast had enough destructive power to break through multiple floors of the hideout, creating a massive hole, but at the very bottom Garou is still standing with his clothes in tatters. Rover quickly fires off more energy blasts, but Garou jumps to dodge them. Rover inspects the destruction at the bottom, but Garou is actually hanging off a ledge above Rover. Garou lets go of the ledge and yells at Rover to sit down, throwing a punch that knocks Rover into the floor, but Rover immediately gets back up, showing no signs of damage. Rover then throws Garou into the floor and blasts him with another energy blast, blasting him through another set of floors beneath them. Garou, still conscious, is buried underneath a pile of rubble directly in front of Gyoro Gyoro, who lifts the rubble on top of him stating that Garou lived up to expectations. Gyoro Gyoro goes on to state that he is very pleased, before paralyzing Garou and commending him on his growth in such a short amount of time.
Saitama suits up and heads out towards the battered streets. Meanwhile, Garou remains restrained by Gyoro Gyoro's psychic powers. Gyoro Gyoro comments on Garou's incomplete monster transformation. Gyoro Gyoro desires to elevate Garou into an even greater monster through a specialized monsterfication process. Gyoro Gyoro explains that in order to accelerate the growth process, the human must repeatably experience death in order to overwhelm the body and spirit. This is a delicate balance as the human can easily succumb to death during the process and even successful candidates will stagnate due to lowered intelligence. The key ingredient needed is for the human to experience their very own personal hell. Garou says that it sounds like Gyoro Gyoro performed this process numerous times, which Gyoro Gyoro confirms. While it is easy to turn humans into monsters, the process simply improves existing abilities the human has and has little to no prospect for further growth. Garou grimly stares on, as Gyoro Gyoro goes into detail about the experiments. From the experiments, the repeated experiences of death allows the person to explosively grow in strength and abilities. Despite this know-how, Gyoro Gyoro never managed to create a monster with a disaster level Dragon except for one.
The scene cuts back to a woman wearing glasses approaching a silhouetted man. She states that the man has turned back on humanity and is going crazy. The scene changes again and the woman looks up towards the newly created Monster King Orochi.
Gyoro Gyoro mentions that Garou has qualities greater that Orochi and through his battle with Royal Ripper and Bug God, Garou has broken through another wall of limits. Gyoro Gyoro then offers Garou to join forces. Garou refuses, but Gyoro Gyoro says he never had a choice to begin with. Gyoro Gyoro reasserts Garou's powerlessness by reminding him of his binding and her psychic powers dwarfing the psychic sisters, Tatsumaki and Fubuki. Nevertheless, Garou begins to take a step as he is getting used to it. This time, Gyoro Gyoro disciplines Garou with force by throwing rocks at him. In doing so, a weakness is revealed in that Gyoro Gyoro can only perform one action at a time and Garou is freed from his binding. Garou then threatens to kill Gyoro Gyoro.
Afterwards, Orochi intervenes, grabbing Garou and pulling him down to eye level with Orochi. The fight then starts, with Orochi firing his horns at Garou, piercing him and leaving a visible round hole in his abdomen. Gyoro Gyoro comments on Orochi's horn manipulation as his first discovery as a monster. Garou defends himself with Water Stream Rock Smashing Fist and stays on the move, killing some monsters as he does so. Garou leaps to attack Orochi head on, but mouths within mouths open up in Orochi's jaw and almost bite down on him. Orochi transforms into a serpent-like being that seems to be a mixture of a hydra and tyrannosaurs rex. The reptilian heads fire a super-heated flame at Garou, incinerating the entire stage. A fist forms from the snakes' appendages and smacks down on Garou, sending him into a wall. Gyoro Gyoro calls for Garou to give up, but Garou refuses, bragging about his status as a genius combatant. He acknowledges Orochi's strength, but claims that he is missing the primal terror that makes him a true monster. Garou utilizes Abandonment, but Orochi copies his stance. Gyoro Gyoro informs Garou that Orochi is a "genius" in the same way Garou, having managed to adopt his style as they fought. The fight renews and this time the dragon appendages all utilize Water Stream Rock Smashing Fist. In the end, Garou is defeated.
Meanwhile, Saitama is looking down a manhole where he is sure he heard sounds from.
The S-Class are having a meeting discussing the Monster Association and their plan of attack. Sweet Mask barges into the meeting and insists that he should lead the S-Class heroes. This antagonizes Tatsumaki, Flashy Flash, and Zombieman. Right before things come to blow, King enters and quells the situation with all their mutual respect for him. Sweet Mask leaves but says that he will be part of the underground strike force.
Sekingar and Sitch are discussing the situation. Sitch is surprised that Sekingar is personally heading to the scene as he thought he was only motivated by fame. Sekingar confirms that he is motivated by fame and he believes that he will be remembered in history in taking down such a threat.
They move down to greet various heroes that arrived by helicopter. Mizuki, Crescent Eyebroll, Needle Star, Gearsper, Narcisstoic, Feather, Jet Nice Guy, One Shotter and various other heroes arrive on scene for a total of 15 heroes. Sitch is informed by staff that Silver Fang had arrived. After he leaves, Bomb tells Bang that they suspect him. King enters the same room as Bang and Bomb to hide in. Bang coaxes out information on the rescue operation and they decide to meet up at Saitama's apartment so they can invade the base on the same route as King. King rejoins the waiting heroes and they leave.
Fubuki walks towards Saitama's apartment while thinking about her situation. She encounters Genos who was thinking over information on his new form. They enter Saitama's apartment only to find Saitama missing. Genos finds his hero suit missing and concludes he must have left. Bang, Bomb, and King soon arrive. They decide to have Genos wait for Saitama at his apartment while the rest head towards the raid. Meanwhile, Saitama is still exploring the tunnel down the manhole.
The heroes strike team arrive at the Z-City Ghost Town. The heroes comment on before getting interrupted by Zombieman's warning up ahead. Numerous monsters, including Evil Eye jump out and surround the heroes strike team. Sekingar expresses surprise over Gyoro Gyoro's underhanded tactics while Feather readies up for battle. Evil Eye mocks the heroes strike team due to their lack of numbers and Child Emperor tallies the number of monsters to over 150. Tatsumaki disregards their numbers while Puri-Puri Prisoner encourages other boys to stay behind him. Evil Eye then telekinetically lifts several buildings. Tatsumaki responds by creating a barrier protecting the strike team but leaves them to deal with the falling debris. Puri-Puri Prisoner and Superalloy Darkshine ultimately save Shadow Ring, Narcisstoic, Gearsper, Green and Food Battler Futoshi from the falling debris. Sekingar angrily questions Tatsumaki on her attitude and she brushes him off, saying that if they can't deal with the debris they should leave, as they will get in the way. Evil Eye declares that he will gouge out the eyes of Tatsumaki and her sister, Fubuki, as an experiment, which angers Tatsumaki. They fight, leaving a great whirlwind behind as the rest of the monsters attack and the support heroes show off their skill. Some notable talents include Twin Tail's Death Loop attack, One Shotter's shooting abilities, Green's Chlorokinesis, Narcisstoic's so called beautiful attacks, Feather's aerial attacks, Shadow Ring's ninjutsu, Double Hole's nose attack, Jet Nice Guy's new cyborg body, Needle Star's skill with his chain mace, Mizuki's killer athleticism, Food Battler Futoshi's surprising agility, Strange Binding Shell's rope movements and Poison's poisoned knife. Sweet Mask comments on Feather's star potential and Flashy Flash asks Shadow Ring where she learned her ninjutsu, to which she answers that it's from a different place than where Flashy Flash learned his. Superalloy Darkshine praises Mizuki's muscles while he blows up some monsters. Gearsper believes he took down some monsters when they were the work of Bushidrill and Okamaitachi, while Sekingar shoots a laser beam from his metallic eye. More monsters show up, but Rhino Wrestler barges his way through. Once a Tiger disaster level, Rhino Wrestler has trained enough to become rated as Demon-level according to Gyoro Gyoro. The support heroes engage him, while up above, Gyoro Gyoro continues to watch the battle with the spy drone. Atomic Samurai then steps into the battle intent on ending it quickly and slashes so quickly that Rhino Wrestler doesn't even notice he's been cut until it's too late. Atomic Samurai then moves on to finish off other monsters and notices Flashy Flash doing the same. Superalloy Darkshine bursts monsters open by simply running through them and Pig God eats a monster. Puri-Puri Prisoner punches a monster to bits and Tatsumaki drops down with the remains of Evil Eye.
Above, Gyoro Gyoro's spy drone is cut in two by Child Emperor. Gyoro Gyoro states that he had already seen the battle, although he would have preferred to see King in action. Gyoro Gyoro's attention is drawn towards the approaching figures where one of them is irritated by her summons. The short black mysterious being questions on why Orochi, Nyan, a rotund looking monster, a scruffy looking man wearing a crown and a fat ugly looking monster were all called.
Meanwhile, Superalloy Darkshine, Crescent Eyebroll and Feather finish off some monsters. Double Hole and Green are administrating some first aid to Needle Star. Mizuki, along with Gearsper, is struggling to push Pig God down the stairs to the Monster Association. Atomic Samurai helps them through and reassures his pupil, Iaian, of his worries.
Gyoro Gyoro rebukes the monsters that ran away from the initial confrontation with the heroes and kills the cowardly monsters by feeding them to Orochi. He warns the remaining monsters to not fail him again and orders them to attack their assigned heroes.
The rest of the S-Class heroes take their routes with Atomic Samurai's Disciples following him. Flashy Flash goes over the information on the transmitter before he runs into Gale Wind and Hellfire Flame. Gale Wind and Hellfire Flame compliment Flash Flash on his speed, all the while Flashy Flash determines who hired them to attack him. Gale Wind asks what if Aburabozu, the king of organ traders, hired him but Flashy Flash denies it saying he already killed him. On top of that, Flashy Flash states he already killed Harold the drug kingpin, heart collector Burigura, phantom thief Chimagusa, the invincible pirate captain Devil Storm and the higher ups of the Coalition of Assassins. Gale Wind reveals their motivations to be ruling the world and that ninjas from their Ninja Village will be the most troublesome opponent. Flashy Flash scores a hit on the monsters and tells them to bring out their monster forms. Unperturbed by the reveal, Gale Wind and Hellfire Flame bring out their monster forms. They continue attacking Flashy Flash and reveal their disaster level as Dragon. With their increased speed, the monsters keep up their pressure on Flashy Flash. However, even after Hellfire Flame utilizes his technique Fire Release: Blazing Scattering Slash, Flashy Flash is able to block it. Flashy Flash uses Heavy Flashy Slash aiming to destroy Hellfire Flame's sword. Gale Wind expresses astonishment at Flashy Flash's technical prowess and the monsters decide to abandon the battle as ninjas and fight using brute speed and strength. The two monsters are able to pressure Flashy Flash, managing to make him cough up blood. However, once the hero became serious, he strikes both of them with a series of kicks, and then slices both of them in half with his ultimate technique Flashy Slash, ending their lives.
After Flashy Flash leaves the battlefield and arrives at a junction, he decides to use his Locator to figure out his location, only to realize that he lost it during the battle.
Child Emperor is walking down a passageway and monitoring what the other heroes are doing. A monster tries to ambush him, only to be shot dead by one of Child Emperor's robots, Mini Octotank No. 8.
He then finds the remains of the destroyed Metal Knight Unit. He is concerned that there may be robotics experts working with the Monster Association and that the technology that was developed to fight monsters may end up being used against the heroes themselves. He then decides to try salvaging some information from the remains of the robot in hopes of finding out where the hostage, Waganma, is being held. The robot yields a detailed map showing where the hostage is held and Child Emperor is angry that Metal Knight has refused to share this information despite knowing it. He then realizes that Octotank has been destroyed by Phoenix Man, who asks if he was here to play. Phoenix Man monologues about his role within the Monster Association and his backstory before attacking Child Emperor, only to run hard into an invisible shield. As the monster reels in pain, Child Emperor executes Phoenix Man with an array of tools that spring out from his backpack. He rescues Waganma by gassing the monsters guarding the hostage's cell while protecting Waganma with a frog-themed gas-mask. As they are about to leave the cell, Sludge Jellyfish oozes in and attempts to crush Child Emperor, only to realize that this is unsuccessful as Child Emperor has put up a shield generated by his umbrella. He tries to cut up Sludge Jellyfish before defeating the monster by dousing it in liquid fuel and setting it alight.
As the two of them escape, he notes that something appears to be up ahead and sends a toy tank as a sentry. The tank is destroyed as Machine God G5 appears. Child Emperor attempts to disable the machine using a high voltage cage and a jamming signal, but G5 defeats it easily. After destroying Child Emperor's Radio-Controlled Sentry, G5 resists the attacks of Child Emperor's Enemy Machine Disabling Device: Bug-Kun and swiftly destroys it. G5 battles the newly combined Underdog Man, Mad Dog Underdog Cerberus, while hampered by Child Emperor's bird lime missiles. As G5 battles Mad Dog Underdog Cerberus, Child Emperor and Waganma escape.
On their way, they come across Phoenix Man's shredded body. Suddenly, Phoenix Man arises into a new, stronger form. Child Emperor confronts the monster and uses 5 layers of his transparent film but is broken through by Phoenix Man's Beak Attack. Frustrated at his uselessness, tears flows down his cheeks and Child Emperor is forced to summon his ultimate weapon, the mech Brave Giant. However, Phoenix Man correctly deduces that the mech has limitations and Child Emperor reaffirms to himself that the monster must be dealt with as soon as possible. Child Emperor uses his Divider Shield and charges at Phoenix Man. Brave Giant locks onto Phoenix Man and launches a volley of heat-seeking missiles, which Phoenix Man is able to prematurely detonate by using Phoenix Flare. Child Emperor then activates Brave Giant's Delta Scale Saber, and slashes at Phoenix Man, who dodges them. Phoenix Man, noting the sloppiness of Brave Giant's attack patterns, initiates his Phoenix Fire Falcon Mode, and circles around the mech suit, now even faster than before. Phoenix Man uses Phoenix Heat Up Talons Strike on Brave Giant several times, damaging the suit. Child Emperor, however, counters by launching Little Braves (autonomous robots) from the armor, which charge up their All Range Attack, and fire at Phoenix Man. The monster changes form once more, this time entering Phoenix Prominence Hawk Mode, and absorbs the attack. Child Emperor, desperate to finish he battle, uses Brave Giant to launch a downward assault on Phoenix Man using one of Brave Giant's swords, but Phoenix Man catches on, destroying the blade. Phoenix Man uses the opportunity to attack Waganma with his Phoenix Homing Wing Attack, forcing Child Emperor to come to the hostage's aid. Brave Giant blocks most of Phoenix Man's attacks, and then responds with suppressing fire from its own machine guns. Phoenix Man resolves to continue distracting Brave Giant and run down its timer, but is suddenly caught in an electromagnetic shield launched by the mech. Brave Giant, still holding Waganma, launches a right hook punch at Phoenix Man, but Phoenix Man is able to catch it. Child Emperor activates Brave Giant's boosters, overpowering Phoenix Man, and sending the trio tumbling through many floors. Child Emperor notices the signal from one of the other heroes' locators, and hopes to meet up with them to finish off Phoenix Man, who he believes will resurrect again. The group suddenly find themselves in the same room that Flashy Flash had just done battle in, and sink into a pool of water. Reaching the bottom, Child Emperor spots a bunch of strange masks resting on the ground and contemplates what occurred, shortly before finding Flashy Flash's locator. As Child Emperor wonders what happened to the hero, something behind Brave Giant explodes, sending the mech suit tumbling through the water.
Phoenix Man revives himself again, and displays his newfound powers by reanimating the corpses of the Subterranean People, Gale Wind, and Hellfire Flame. While Child Emperor deals with the undead army, Phoenix Man takes Waganma and starts flying away. Child Emperor finishes off the army and races after him, launching an all out energy beam on Phoenix Man. Phoenix Man withstands the energy beam, and his costume changes again, gaining withered patches on half of his body. Child Emperor then opens the robot's emergency hatch, and has the Little Braves close it on Phoenix Man, trapping him. The monster easily rips the mecha apart but Child Emperor managed to sneak in a tickling robot within Phoenix Man's costume while he was trapped, stating that the robot would tickle him until he died of asphyxiation. Phoenix Man hastily attempts to get rid of the tickling robot by ripping his costume. With the costume ripped, Phoenix Man loses his powers and Child Emperor proceeds to kick him in the groin before tearing off the rest of the costume to ensure he doesn't revive himself again. Phoenix Man lies defeated as Child Emperor turns to Waganma asking him if there were any other hostages, but Waganma decides not to tell Child Emperor that Tareo was taken too.
Zombieman travels through the Monster Association HQ on his strike route and eradicates all the monsters he encounters. He meets a crowd of monsters that direct him into a room, stating that they won't attack, and only want him to fight something. Zombieman complies and walks into the room, where he encounters Vampire (Pureblood). Despite suffering many fatal wounds, Zombieman continues battling until he kills Pureblood. After the battle, he remarks that he hasn't fought someone as strong as Pureblood for some time, and that it had left him tired. The hero bends the door's bar around the handles to lock the room, and turns to wipe out the remaining monsters who had watched his fight with Pureblood. He walks out of the room having killed all of them, then decides to sit down for a bit to heal himself and smokes a cigarette while checking his Locator.
Child Emperor reports that he has rescued the hostage, Waganma, and is bringing him to the surface. Child Emperor orders all heroes are to continue their assigned mission, but warns them not to venture too far into the Monster Association HQ. Zombieman finishes his break and stands up fully healed, then continues down his strike route.
Pig God comes across The Great Food Tub. Their sounds of battle are overheard by Iaian, Bushidrill and Okamaitachi. They refocus their attention on the mind controlled Mercenaries and Do-S. The mercenaries attack the heroes and while distracted, Do-S aims to mind control Bushidrill with her whip. The whip is snatched out of the air by Sweet Mask and he calls on the sword heroes to move on as he deals with them. Iaian and Bushidrill protest, unsure of letting Sweet Mask fight them by himself, but Okamaitachi convinces them to move on and let Sweet Mask fight in their place.
The three disciples decide to trust in Sweet Mask and retreat, leaving him alone to face Do-S and the brainwashed Narinki Squad. Do-S tells Sweet Mask that she is actually a fan of him, and offers to 'unbrainwash' the slaves in exchange for spending time with him. Sweet Mask tells her that bargaining won't work against him. Do-S responds by ordering her slaves to attack the hero, while the disciples dash off to another area. Sweet Mask effortlessly tears through the entire Narinki Squad, subsequently killing all of them. He continues to charge towards Do-S, who is shocked at how Sweet Mask dealt with the mercenaries. She attempts to brainwash him by striking him with her whip, but fails to do so as Sweet Mask is somehow immune to such attacks. Realizing this, Do-S quickly surrenders and submits to Sweet Mask, promising that she will obey his every command. Unmoved by Do-S' plea for mercy, Sweet Mask takes her life.
The scene cuts to the disciples staring in shock at Pig God, who was in the midst of digesting The Great Food Tub. The three disciples then agree to find another way into the base. Slicing up the ground below them, they descend to a lower floor and encounter the mysterious beings, Devil Long Hair. Okamaitachi is romantically tempted by the monster's good looks but restrains himself to send an Air Blade at him. The monster blocks it with his hair and strikes at the heroes from underground. The heroes work together to strike at his hair while recalling Atomic Samurai's words of advice.
Meanwhile, Puri-Puri Prisoner is engaged in combat with several monsters. A large blast occurs, and the monsters laugh thinking they have finished off their opponent. As the dust clears, we see a glimpse of a seemingly intact Puri-Puri Prisoner. Various monsters find that their attacks on Puri-Puri Prisoner to have no effect regardless of their variety. Puri-Puri Prisoner explains to them that embracing the pain with love allows him to take those hits. He dubs his power Angel ☆ Hug. Realizing their strength wouldn't be enough, the monsters flee only to be stopped by the Demon-level monster, Vacuuma, who inhales the fleeing monsters, absorbing their powers. Vacuuma then fires a variety of attacks at the hero, but Puri-Puri Prisoner remains undeterred. The monster mocks him, but, the hero completely smashes through Vacuuma and ends the monster's life.
Soon after, Puri-Puri Prisoner hears the voices of the monsterified inmates and expresses dismay at his inmates predicament. Believing the inmates to be forced to do the Monster Association's bidding, he vows to save them. The inmates attempt to explain their hatred to Puri-Puri Prisoner but he continually ignores it. Nyan then interjects and says that once a human becomes a monster, they will never turn back, before slashing Puri-Puri Prisoner, severely injuring him, and leaving the rest to the inmates. Puri-Puri Prisoner stands strong, however, and declares that as long as the heart is human then they will always be human. Nyan, disturbed by Puri-Puri Prison's strange personality, decides to leave him to the other cadres and escapes through a narrow crack. Puri-Puri Prisoner gives chase after thinking up a new technique, Angel ☆ Crawl, but accidentally crushes his fellow inmates in debris, killing almost all of them. He loses his armored hair and accepts their sacrifice by avenging them.
Puri-Puri Prisoner is left exasperated over Nyan running away and carries on his way. Superalloy Darkshine encounters Bug God and was initially discouraged at Bug God's boast but is let down by the monster's weak strength. Superalloy Darkshine tells the monster that along with King and Tatsumaki, he is one of the three heroes you must never anger. Bug God transforms into a new form, growing 4 extra arms and wings, but Superalloy Darkshine destroys the monster in one hit.
Saitama is wandering through the Monster Association HQ and fights Overgrown Rover. Saitama punches the monster, shaking the entire headquarters and the ground above. Nyan attempts to assassinate Saitama with Super Feline Retribution but the hero is unfazed and the monster escapes underground.
Gyoro Gyoro contemplates over Saitama's attack before Tatsumaki appears. Gyoro Gyoro then crushes Tatsumaki under a globe of rocks and compresses it but Tatsumaki breaks free easily. The hero sends a rock, blasting through Gyoro Gyoro's barrier and bursting its arm. The monster reveals its true form and many eyes open around its body. Gyoro Gyoro sends a Super Gravitional Wave that multiples the gravity in the region by 300. Tatsumaki remains unimpressed and destroys the monster's body. Gyoro Gyoro pretends to be on the throes of her death, but Tatsumaki sees through the meat puppet act and declares that she will pull out his real body. Gyoro Gyoro, regretting his grave miscalculation to battle Tatsumaki, calls upon Orochi to assist. However, there is no response. Deprived of his last option, Gyoro Gyoro attempts to bargain with the hero.
Meanwhile, Saitama looks down upon a great hole in the Monster Association HQ. At the bottom, Orochi climbs up fully transformed and confronts Saitama. Saitama questions just why the creatures are living under his home and Orochi declares his acknowledgement of Saitama's threat. Saitama tells Orochi that he is merely a person who lives above ground. Orochi then attacks Saitama with his horns and notes the impact he felt earlier was from Saitama and that he was not on the Monster Association's warning lists. He then states that if Saitama is not defeated here and now, it will become very dangerous. Orochi breathes fire on Saitama, which he narrowly dodges. Overgrown Rover then awakens and Orochi orders him to dispose of the intruder. However, Rover, recognizing the agent of his defeat quickly runs away from the fight. A surprised Orochi then asks Saitama what he did to Rover, and Saitama responds by saying he beat him up. Orochi realizes that Saitama is the reason for Gouketsu and Elder Centipede's demise, and remarks on how excited he is, and then transforms into a more humanoid form. He then states that he is curious to see what Saitama as a dueling partner with immense strength has to offer him. Saitama then states that despite what monsters say, about them being the "ultimate life-form" they all fall to one single punch from him. Orochi then attacks using the dragons on one of his arms. They are all quickly felled by Saitama. The dragons from his other arm all generate a massive beam of electricity that destroy the ground and create a massive tunnel. This surprises the other S-Class heroes, who defend themselves from the electricity. The tunnel destroys a subway line and the confused driver questions what had happened as he sees Saitama speed by. Saitama then destroys Orochi with a single punch. Orochi's shattered head questions what it was that just hit him, and Saitama responds by saying it was a normal punch. Orochi, now knowing terror, then falls into the abyss below, defeated.
A defeated Gyoro Gyoro is searching for Orochi using his eyes. On realizing he has perished, Gyoro Gyoro looks around for the man who defeated him. The eye finds Saitama and is promptly crushed by him, but not before Gyoro Gyoro notes his bald appearance. On hearing of this description, Tatsumaki wonders if Superalloy Darkshine is the hero she is referring to. Gyoro Gyoro disregards this and questions if Orochi is dead. Tatsumaki tells Gyoro Gyoro that he does not have the luxury of worrying about others, due to his current state. Gyoro Gyoro then begs for his life. Tatsumaki, recognizing that Gyoro Gyoro is just a meat puppet, tells him to come out of his shell and apologize. Gyoro Gyoro then raises all the eyes that Tatsumaki had ripped out and fires several beams of psychic energy at her. This is easily deflected, although Tatsumaki does state that it was an elegant and nuanced use of her psychic ability and asks who taught him how to do it. The "real body" is then ripped out of the meat puppet, and Tatsumaki recognizes her as a friend of Fubuki.
At the same time, Fubuki, Bang, and Bomb are seen walking along a hallway, when Fubuki suddenly stops, feeling her sister Tatsumaki using tremendous amount of her psychic powers. She also states that it is very rare that she would have to exert herself to such an extent, leading Bang and Bomb to state that they have to be more vigilant regarding the strength of the monsters that they may face.
King is wandering the hallways of the Monster Association alone after splitting up from Bang, Bomb, and Fubuki. He then hears someone calling his name, which startles him. He turns around and realizes it's the hostage, Waganma. Waganma says that a monster is chasing him, and tells King to finish it off and carry him to the exit. He then asks to hug King, but when he is about to do so, the King Engine starts beating and King tells him to find another hero, stating no matter how sweet and cute Waganma acts, it's not possible for King to protect him. At this point, Waganma is revealed to be a shapeshifting monster, who, interpreting King's words as it's cover having been breached, promptly dies of fright. King, too, notes that that was terrifying and that he needs to find Saitama.
Meanwhile, Iaian, Okamaitachi, and Bushidrill are shown battered from their battle with Devil Long Hair. Having cut through every strain of Devil Long Hair's locks, he collapses commenting that it was his Achilles heel. Surprised by their victory, the disciples comment that they would not have won individually and worry that more monsters of that level may exist.
Atomic Samurai is cutting down several monsters when a sword wielding monster, Sword Devil Executioner, praises Atomic's skill. Surprised a monster survived his slash, Atomic Samurai cuts his opponent down before the monster knows what happened. Atomic asks any monster not yet dead to raise their hand. G5 raises his mechanical arm and says that he has analyzed all of Atomic's moves and they begin a high-speed sword duel. Atomic comments that modern day "toys" have become interesting and says that he'd like to buy one, prompting G5 to increase his speed. G5 confidently proclaims that he will beat Atomic in 23 moves but fails to do so. Atomic slices his foe into hundreds of pieces but says that he didn't cut the core of the Machine God as it was a harder material. A laser beam shoots from the cloud of smoke but Atomic deflects it and sends an air blade of his own to counter. As the air blade penetrates the smoke, Atomic realizes that the real opponent has escaped, saying he'll leave it to the surface team of heroes.
The scene changes to Child Emperor and Waganma who are nearing an exit of the Monster Association HQ. Waganma asks Child Emperor to escort him all the way back to his father, but Child Emperor states that the surface team will perform the task as he wants to return to the battles below.
Tareo is being chased by Black Sperm, when a slash from Atomic Samurai stops the monster, forcing him to dodge.
Through the communication device, Child Emperor notifies the other heroes that he has rejoined the Surface Team and that the hostage rescue mission is successful. He then realizes there's no response coming from the communication device and asks if anyone can hear him but there is still no response. Worried if anyone received the message, Child Emperor then asks Sekingar if he explained to everyone how to use the communication device. Sekingar just says to give the heroes some time, thinking they probably can't answer as they're in a battle. As he finishes speaking, there is a response from the communication device from Zombieman who praises Child Emperor for a job well done. Child Emperor is happy that Zombieman responded and in that moment, Sweet Mask responds too, saying that he will continue to carry out justice. The next hero is Pig God who, while digesting something, also praises Child Emperor and notes that nothing's out of the ordinary. The final voice that's heard in that moment is Atomic Samurai's. Atomic Samurai is confused as how to use the communication device. He explains that he found a kid inside the base, much to Child Emperor's surprise. Child Emperor tries asking Atomic Samurai to describe the kid but is unable to, as the transmission cuts off.
Child Emperor then turns menacingly to a scared Waganma, asking if he had known all along that the monsters may have captured other hostages. Waganma starts to cry, telling them that he wanted to be rescued and that he's sorry. Child Emperor then grabs his backpack, saying he has to go and leaves Waganma to the other heroes. Sekingar tries talking Child Emperor out of going back, pointing out the hero is exhausted and that their priority of rescuing Waganma has been completed. The other heroes try to offer their assistance, but Child Emperor turns them down, stating that they should all stick to their assigned tasks. Needle Star then thinks to himself in awe about S-Class heroes, reluctantly acknowledging the gap between them and the rest of the heroes.
Black Sperm gets angry at Atomic Samurai because Atomic Samurai attacked him without warning. Atomic Samurai then gets cocky and says that he had no business with him and Black Sperm grows an enormous muscular arm and asks if he is looking down on him. Atomic Samurai answers his question with a "yes," before swiftly cutting the arm and mentioning that he's fought countless battles with similar bastards who can transform and shape-shift into giants, and that he's used to these opponents. A second Black Sperm then appears from what was once the cut arm behind Atomic Samurai and Atomic Samurai gets annoyed. Black Sperm then asks Atomic Samurai if he still thinks he has a chance to win, noting that he's a countless number of "Black Sperm" merged into one entity and saying that no matter how many times he's killed, he'll keep multiplying. As the pieces begin to quickly surround Atomic Samurai and regrow into new selves, Atomic Samurai just slashes them again. However, they just reappear, in ever larger numbers, jumping on him and getting slashed into more pieces until eventually, Atomic Samurai finds himself faced with a massive number of Black Sperm clones, completely surrounding him in every direction, as Black Sperm tells him that he has already lost the fight and is going to die. The Black Sperm clones then begin to gain the upper hand on Atomic Samurai, who is shocked to learn that the monster's strength has not diminished at all, even after splitting into numerous copies. Outnumbered and surrounded, Atomic Samurai realizes that he has underestimated his opponent and begins to withdraw from battle after getting overwhelmed. He manages to create some distance between himself and the swarm of clones by carving a hole in the ground directly underneath him and entering free fall, with the Black Sperm clones following suit, mocking him. However, one of the clones is completely destroyed by an attack in their pursuit. What was to them an escape was actually the hero's attempts at drawing them into a closed space for him to attempt a type of attack that can deal with enemies with powerful regenerative capabilities, a Focused Atomic Slash capable of totally destroying monsters with the ability to regenerate.
Having used the rest of the free fall to destroy the pursuing clones with his new technique, Atomic Samurai finally hits the ground, remarking that his enemy was tough enough to force him to use his new technique. He then remembers that the monster had been chasing a child just before their battle and makes his way back up, only to be caught off guard by an enormous Black Sperm ready to attack. The monster says that the clones Atomic Samurai had killed were but a fraction of his total being, having hid his true form from the very beginning. Atomic Samurai barely manages to counterattack the enlarged monster, getting hit in the process. His slash only results in more Black Sperm clones emerging, who continue to taunt the injured hero, telling him that he is in the "worst possible match-up" formulated by Gyoro Gyoro. Heavily injured and out of options, Atomic Samurai quickly cuts at the roof, resulting in the ceiling collapsing in on all of them.
The ensuing collapse results in powerful vibrations felt by Zombieman who expresses concern over how the battle may be going for other heroes. Without warning, Homeless Emperor appears behind him and blasts him point blank with a beam of energy. Homeless Emperor then expresses disappointment over how quick Zombieman was killed, before going on to state that he will kill all seventeen of the S-Class heroes alone. A regenerated Zombieman then lunges at him with with an axe, only to be shot in the head with a concentrated energy blast. His opponent disabled, Homeless Emperor stares at his decapitated body, a sudden gunshot coming from his upper body. Homeless Emperor unflinchingly counters the attack, while Zombieman is blown away and crashes into a wall, questioning how he would be able to react to such a shot at close range. Dismayed at how his hidden ace had failed, Zombieman regenerates and removes the pistol stored within his body, firing several shots at his opponent. Homeless Emperor counters with several orbs of energy, sending them all towards the hero, resulting in a large scale explosion. As the smoke clears, Zombieman's charred body stands before Homeless Emperor, who compliments him.
Zombieman asks Homeless Emperor what he is, partially because he has no idea how his attacks worked, but mainly as a way to buy time for his body to regenerate because Homeless Emperor is too strong. Homeless Emperor says that, until a month ago, he was living at the park. He had lost his job, gotten kicked out by his landlord, distanced himself from human society and began living as a hermit. He recalls being forced to dance naked in front of his boss at the new employee welcoming party only to get fired the next day for sexual harassment. But when he stared at the sky, the resentment he felt towards his boss and other such things no longer seemed to matter to him. For to him, the Earth was greater than any man-made structure and the sky brighter than any man-made light. Humanity was an insignificant existence on the great earth. Homeless Emperor saw his true home as the Earth itself, which was grander than any mansion. Then one day, Homeless Emperor had a life-changing realization. He realized humans have abandoned the ecosystem Mother Earth built up and thrived under new, self-made rules. He could no longer bear the reality of it, which left him borderline suicidal as death was the only way to return to true coexistence with Mother Earth. Right then though, an entity Homeless Emperor claims to be 'God' appeared before him. 'God' says Homeless Emperor's view on humans was correct but he had no need to die and says he would grant him power and that he should know what to do with it. Homeless Emperor then says that his power is a divine power granted to him by 'God' and the reason he was chosen was because he knew "the answer" which was that humans were a harmful existence to the planet and that the time has come for him to destroy the entirety of its existence and civilization. Zombieman asks him why he believed the entity to be God and asks if he had 'identification' while thinking that the situation is bad because his body had not finished fully recovering before he was done talking. Homeless Emperor, knowing Zombieman was doubting the existence of God in his story, says there is no need for him to believe in God, and his price for his arrogance will be his death. Saitama is then seen feeling shaking from what was presumably Homeless Emperor wreaking havoc, and worrying about the integrity of his house and it's foundation.
Sweet Mask says to himself that according to Atomic Samurai's message, there was another kid held captive. He then thinks that the battle will take longer than he had imagined and the things he had planned in the future had to be cancelled or rescheduled. While holding a monster head that was still alive, Sweet Mask then stops and asks the monster head what was in front of them. The head says that these were devices were used to nurture monster cells collected from Orochi and that they have the ability to turn humans into monsters. Sweet Mask then thinks that they should just eliminate Orochi to stop their production, but the monster head says that such a thing is not possible. Sweet Mask then proceeds to destroy the equipment.
As he is walking away from the aftermath, something is heard laughing around at the end of the hallway, excitedly saying how it found him. Sweet Mask asks the monster head who the voice belonged to and the head, recognizing the voice as a cadre, says that it is over for Sweet Mask. The monster is then seen bouncing around towards Sweet Mask, and the hero flings the monster head he was using to answer his questions at the cadre, only for it to get kicked straight up at the ceiling. Sweet Mask says it had great movements but he had confidence in a fistfight, only to back away once he sees the monsters face. He asks Sweet Mask why he is so scared even though he came knowing it was the Monster Association HQ. He then recognizes the hero in front of him as Sweet Mask, and says that he's going to kill him. He also says that he is going to carve the reality that looks and battle stats do not go hand in hand and threatens to use Sweet Mask's face to do so. His name is revealed as Fuhrer Ugly and his disaster level as Dragon. Sweet Mask thinks that without a doubt the guy is some type of Ugmon. Sweet Mask realizes this battle is unwinnable for him, because when he sees extreme ugliness, he starts shaking and is no longer able to move.
A monster watches in horror as Pig God devours his monster comrades after mistakenly thinking that the hero would have been a good feed for them. Pig God grabs the monster and puts it into his mouth as it screams desperately. Gums then sneaks up from behind Pig God and swallows the hero. Pig God struggles to escape, and Gums is forced to spit him out. The two then battle.
The scene then shifts to a monster, limping away from the Disciples of Atomic Samurai after being wounded by them, who mentions unleashing something. Iaian, Bushidrill, and Okamaitachi are walking down a corridor when Bushidrill notices a dangerous aura coming from a room they are near and asks if the others sense it too. As they enter the room, they see a water tank with fish in it. The monster then informs them that even Gyoro Gyoro had difficulty controlling the thing in the tank and adds that it was a cadre, before recklessly pushing the tank over and unleashing Evil Natural Water. The fish inside the water immediately eat away at the monster, and they are revealed to be Mad Doctor Fish. The monster desperately tries to reason with them but the water swallows it up and the fish turn him into bones, while the three swordsmen watch in shock. The Mad Doctor Fish attack Iaian, who swiftly cuts them down. Iaian notes that although the fish are no problem, the situation is hopeless because they had no way to cut Evil Natural Water.
Puri-Puri Prisoner continues his search for Nyan as he "swims" through the underground walls of the Monster Association base. He ends up in a small chamber filled with torture equipment and notices Garou chained to the wall, seemingly unconscious. Not recognizing Garou as the infamous Hero Hunter, Puri-Puri Prisoner thinks he's simply another human hostage and moves to release him. However, just as Puri-Puri Prisoner recognizes Garou's face, Garou awakens and breaks the chains before swiftly pummeling the hero. The S-Class hero quickly understands the grave mistake he made by awakening the mysterious prisoner.
Elsewhere, Saitama continues to wander through the Monster Association base as he searches for someone to talk to about all the noise under his apartment. He is ambushed by a monster, and swiftly kills it with one punch. Around the next corner, Flashy Flash lies in wait. He gauges Saitama's size and deduces that he must be a monster, so he dashes around the corner and slashes at his target. However, Saitama easily dodges. Flashy Flash is shocked to recognize Saitama as the B-Class hero who once accompanied Genos to an S-Class meeting in the past. Enraged that he dodged his surprise attack, Flash performs his special Flashy Slash move on Saitama, who simply catches the sword in one hand. Unamused, Saitama accuses Flash of being a monster for attacking him, so he quickly clarifies that he's a hero too. Flash explains that they are in the Monster Association's territory, and tells him he should find shelter. Flash also tells him of the existence of the Monster King Orochi, exciting Saitama as he doesn't realize he already killed him earlier. Annoyed by Saitama's persistence to stick around, Flash runs off at high speeds to abandon him, but is shocked when Saitama can easily keep up with him. As they run, Saitama notices how he is seeing the same monster corpse and section of the halls again and again. Saitama asks Flashy Flash if he is lost, only to be ignored by the annoyed ninja.
Outside, multiple A-Class and B-Class heroes are battling several monsters to keep Waganma safe from the Monster Association. As the battle dies down and the monsters are eventually defeated, the seal all possible entrances for monsters to emerge. As they voice that victory may be imminent, Poison notices a monster in the distance. He orders One Shotter to fire at the monster, only for the bullet to be intercepted by Nyan's claw and deflected back at the sniper, wounding his head. Nyan voices his joy at coming across a weak group of heroes, after meeting Saitama, and insists they "play" with him. Jet Nice Guy states how they must be cautious when Nyan suddenly appears at the center of them and slashes, wounding him, Needle Star, Gearsper and Twin Tail. Nyan announces that he is a cadre of the Monster Association, while muttering to himself how he has left it already, to the shock of the heroes. He speaks about his past as a normal cat that "played with toys till they broke", now free as a monster to do what he pleases. Sekingar orders Food Battler Futoshi to take Waganma to safety. Feather and Poison take a fighting stance as Nyan eerily grins, stating the theme of this "game" is to rip Waganma apart while the group watches. Mizuki takes her medal, transforms it into a discus and prepares to launch it at Nyan, while Green restrains the monster with his vines. Nyan, with his great speed, catches the disc in his teeth and shatters it. Poison tries to attack Nyan's face, but his blade is stopped by the cadre's eyelid and promptly broken as well. As Feather and Shadow Ring try to attack the creature, Nyan slips out of the vines and shatters their blades instantly. Before the heroes could register what had just happened, the cadre severely wounds the duo, defeating them. As the remaining heroes stare in shock at the devastation, Nyan eyes a terrified Waganma and wonders where they are heading. Seeing the creature staring at him, Waganma orders Food Battler Futoshi to stop eating and speed up, only to be informed that he must eat to replenish his energy supply. Mizuki attempts to stop Nyan from pursuing Waganma and Food Battler Futoshi, but the creature strikes Mizuki into the air. Gearsper cushions her fall with his awakened psychic powers and uses his remaining power to launch an attack at Nyan. He breaks multiple nearby buildings apart, forms the rubble into sharp projectiles, and throws them at the monster, burying it. After the extreme attack, Gearsper's helmet breaks, and he collapses.
Waganma gloats about the apparent victory of the heroes. However, Nyan uses his supernatural dexterity to escape the pile of rubble and quickly slashes Food Battler Futoshi's stomach. The monster tells Waganma that his disaster level is Dragon, terrifying the child so much that he wets his pants. Nyan drags the two away so he can kill Waganma in front of the other heroes. Suddenly, a high-speed projectile breaks the monster's hold on Futoshi and Waganma. The projectile circles back and appears at the hands of Drive Knight. Waganma and Food Battler Futoshi run for safety, while Sekingar watches from a distance, thankful for the arrival of the S-Class hero. Drive Knight uses Tactical Transformation: Chariot and lunges at Nyan. The hero circles around the monster and sprays an anesthetic gas in an attempt to immobilize Nyan. He then charges Nyan with his bike, but the monster dodges through a crack in the ground. Drive Knight releases a strong solvent into the ground that forces Nyan back onto the surface. The hero launches several missiles at Nyan, which the monster easily dodges. Nyan goes for a direct attack, but Drive Knight uses Tactical Transformation: Knight and kicks the monster into the air. He uses Tactical Transformation: Flying Chariot to propel himself above Nyan then transforms into Bishop and punches Nyan into the ground. Nyan slips into Drive Knight's suit and slices it apart using Feline Retribution. Drive Knight then uses Tactical Transformation: Gold. Nyan unleashes flying slashes at him, but the hero is unharmed due to the strengthened armor provided by the transformation. Nyan slips into Drive Knight's body and attacks the hero from unpredictable angles. As Nyan is about to release Feline Retribution in the hero's body, Drive Knight raises his temperature to an extreme level and forces the monster out. He holds Nyan in a chokehold and uses Silver to stab the monster in the torso from behind. Drive Knight then incinerates Nyan.
Sekingar marvels at the strength of Drive Knight after witnessing his battle with Nyan. He questions Drive Knight's actions, but the hero excuses the questioning and displays intel on the Monster Association. He tells Sekingar that Bofoi is a traitor to the Hero Association, sowing seeds of doubt in his head. The executive phones the Hero Association to warn them of Bofoi, but G5 appears and shoots his hand off. Before the robot can strike Sekingar, Genos appears out of the sky and stomps it, causing G5 to explode. He then inquires about the situation.
Genos takes the support team and Waganma to an area guarded by the Hero Association defeating several monsters on the way. While the other support heroes are being treated for their injuries, Sekingar starts tending to his own wound and calls Sitch to tell the latter that Waganma has been successfully rescued. He then tosses the phone to Genos, who has a short phone conversation with Sitch. Sitch thanks the hero for his work and apologizes for leaving him out of the initial battle plan and starts to ask for a favor. In a flashback, Drive Knight takes Nyan's body away for examination. Nyan, who is revealed to be still alive, mentions someone who can defeat Monster Association executives with one punch, and Genos realizes that Saitama is fighting against the Monster Association. Genos tells Sitch that he has no intention of following any orders from the Hero Association and hangs up.
Genos then entrusts Waganma in Food Battler Futoshi's care and prepares to enter the Monster Association hideout. Sekingar hands Genos Monster Association intel provided by Drive Knight.
Superalloy Darkshine finds Puri-Puri Prisoner defeated on the ground. Puri-Puri Prisoner warns Darkshine about Garou, who appears at the end of the corridor. Darkshine and Garou face off.
Child Emperor finds Atomic Samurai's disciples defeated by Evil Natural Water. He dodges the monster's attacks and assembles his snowman robot. Evil Natural Water shoots jet streams at Child Emperor, but the hero counters using his robot's Flash Freezing Breath to freeze the monster's attacks.
Child Emperor continues fighting Evil Natural Water. Sludge Jellyfish enters the room and offers to assist Evil Natural Water, but the monster sucks the oil out of him instead. This renders Child Emperor's freezing attack ineffective due to the oil's low freezing point. The hero is astonished by the brainless monster's ability to optimize the situation. The scene then cuts to show Genos making haste to the Monster Association Headquarters, reviewing the data Drive Knight provided to Sekingar as he does so. He notes that all the cadre are troublesome opponents and that there is no time to come up with any good strategies, although it's possible that Saitama has already killed them.
Elsewhere in the Monster Association base, Flashy Flash and Saitama run in circles, neither having any sense of direction. Saitama suggests contacting the other heroes, but Flashy Flash comments that the other S-Class heroes are competent. A narrator explains that the S-Class was created to group together heroes that were consistently capable of defeating monsters with disaster level "Demon".
All the S-Class are overwhelmed and on the brink of death thanks to Gyoro Gyoro's analysis matchups. Tatsumaki locates Gyoro Gyoro's real body and begins pulling her out, while the villain wonders which executive is free to come to save her. She thinks of Overgrown Rover, but the dog is revealed to have engaged in combat with Bang, Bomb, and Fubuki. Bang, Bomb, and Fubuki fight off Rover. Fubuki shields the martial artists from one of the executive's blasts and uses her psychic powers to improve their physical attributes. Bang and Bomb finish their combination attack on Overgrown Rover, while Fubuki sits there amazed by them both. But she is especially amazed by Bomb, whom she previously thought was just a normal old man, and tries to recruit him to her group, but is interrupted by Rover who gets up uninjured and lively after Bang and Bomb's combination attack. In frustration, Bang asks the dog to sit and behave and to their surprise the monster obliges and they quickly pass.
Meanwhile, Flashy Flash and Saitama are riding around in a minecart trying to get to the Monster King's lair, led by a monster who plans to drop the cart and take them to their deaths at a switching point. But after seeing how far the drop is, the monster is too scared and doesn't do it.
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Tatsumaki reaches the leader, Psykos, and rips the entire base out of the ground. She fights against the Dragon level monsters, but is attacked from behind by Psykos, weakening her. Genos, King and Fubuki arrive to help. Upon reaching the top, Fubuki battles and defeats the leader of the Monster Association who is revealed to be an acquaintance of hers and also a psychic.
Afterwards, Garou appears, having become immensely powerful from his many battles, and evolved into a borderline monster himself. Fubuki is not harmed, but is left in total fear of Garou's might. Garou incapacitates several S-Class heroes and Dragon-level monsters before taunting the heroes who are unable to fight, threatening that he will kill the child he had once saved from being bullied.
At this point, Saitama approaches him with the complaint that he is being a disruptive neighbor. He states that he is going to beat some sense into Garou, who attacks with the thought that Saitama cannot withstand the attack. The result is that Garou is hit with a punch that sends him skipping across the ground. Garou utilizes his martial arts prowess to briefly appear to be overtaking Saitama, but Saitama grows bored and tells Garou to truly fight all out, demonstrating how serious he himself can be by flipping the entire Monster Association HQ once again.
In the debris, Garou becomes disoriented and is beaten badly by Saitama. Upon landing on the ground, he becomes frustrated and more desperate, trying to damage Saitama in any way that he can. After failing and taking another powerful hit, he evolves into a complete monster and attacks Saitama, only to be defeated in one punch, resulting in another evolution that is swiftly dispatched as well.
After a long spiel about his philosophy, Garou demands that Saitama explain why he is a hero. Saitama's simple answer irritates him into yelling more, and Saitama shatters the remaining monster mutation left on Garou in frustration. He states that Garou had an ideal image of a hero in his mind the entire time, and suggests that Garou wanted to be a hero all along, but choose to become a monster that simply had to kill every hero and unite the world against him.
The heroes attempt to kill Garou, but Saitama stalls them and Bang attempts to punish Garou. After the child Garou saved intervenes, Garou becomes filled with a desire to live on and flees the scene.