Monster Raid Arc is the thirteenth arc of the series, and the fourth arc of the Human Monster Saga.
The Hero Association staff members begin to discuss about the threat that Garou poses and how he recently began attacking staff members. The association agrees to assign heroes to protect its cadres when they are in public. Garou is seen in a shack with a wall of photos of heroes he possibly wants to fight.
The Hero Association begins assigning heroes to their new assignments by calling King, but King declines the request, replying that he is already busy fighting a monster when in reality he is just playing a video game. Afterwards, Metal Bat is seen paired with protecting Narinki, a sponsor, and his son Waganma at the Mouse Sushi restaurant in S-City. It is revealed that, unlike King, Metal Bat wasn't even given a choice. Waganma begins trying out the different foods at the restaurant, but he constantly puts the dishes back, even when Metal Bat tells him not to. This cycle slowly starts to frustrate Metal Bat until his sister calls. She asks him to help her with her shopping bags, but he declines because of his mission. His sister ends the call crying and Metal Bat makes a remark saying that he should be the one crying.
Suddenly a rumbling occurs and Metal Bat rushes back to the sponsor. Junior Centipede and Venus Mantrap emerge from the ground and grabs Waganma. The pair of Monsters appears to be looking for Narinki because of his connection with the Hero Association. Before the pair can leave, Metal Bat prepares to fight them.
Back at the C-City Super Stadium, Saitama attempts to sign in.
Saitama is in Charanko's waiting room looking over a list of the contestants of the tournament. He is greeted by a man who seems to know Charanko.
The man turns out to be Sour Face, and he discusses a tournament incident that happened in the past, when Garou decided to win the martial arts tournament under the identity of Wolfman. Sour Face also elaborates that he wishes to win the tournament so that he will never be intimidated if he ever faces Bang or Garou in the future. Furthermore, he talks about the day when Garou rampaged through the dojo. Saitama implicitly states that what Sour Face is doing is pitiful. Sour Face leaves the waiting room feeling aggravated.
Metal Bat has just finished his fight with Junior Centipede and Venus Mantrap. Narinki and Waganma are delighted and wish to celebrate. However, Junior Centipede was still alive, he questioned Metal Bat about how high Metal Bat is in the food chain. Before Metal Bat could finish Junior Centipede off, Senior Centipede erupted from the ground. Senior Centipede forced Metal Bat, the sponsor, and the sponsor's child out of the restaurant. Outside, Rafflesidon emerged from the ground and started releasing gases to knock people out. Garou is with Tareo near the outside edge of S-City. Tareo informs Garou about Watchdog Man's whereabouts and routine. Suddenly the city announces a disaster level of Demon and that Metal Bat is busy fighting monsters. Garou decides to pay Metal Bat a visit.
Metal Bat is fighting Senior Centipede and Rafflesidon. Metal Bat and the two monsters seem to be fighting on equal ground until Rafflesidon begins releasing gases causing Metal Bat to enter a drunk-like state, unable to fully control his movements. Senior Centipede takes this opportunity to injure Metal Bat. However, Metal Bat is able to eventually escape the state by damaging his head, an action that surprises the two monsters. Senior Centipede decides to go for a finishing blow, but Metal Bat detaches Senior Centipede's arm. Metal Bat then proceeds to defeat the two monsters with a single strike each.
After defeating the demon level monsters, B-Class and C-Class heroes, Pineapple and Mohawk, arrive at the scene. Metal Bat asks them to bring the Hero Association's sponsor and the sponsor's son to a hospital so that he could finally help his sister with her shopping bags. However, Elder Centipede emerges from the ground. The lower class heroes inform Metal Bat about the monster, stating that it previously wiped out a town and it is marked as a dragon level monster. Metal Bat tells the two other heroes to grab the sponsor and the sponsor's child and run, while he prepares to go all out.
Metal Bat is deciding how to handle the situation when suddenly Elder Centipede attempted to get the Hero Association sponsors. Metal Bat managed to intercept Elder Centipede. However, Metal Bat's swing did not manage to injure Elder Centipede and Elder Centipede launches Metal Bat to a building.
Metal Bat jumps onto Elder Centipede while Elder Centipede is chasing after two heroes to get the Hero Association sponsor. Before Elder Centipede is able to reach the two heroes, Metal Bat unleashes an attack on Elder Centipede's head. Elder Centipede then tries to shake Metal Bat off by with maneuvering around the city. Garou finally arrives to the scene just when Metal Bat is launched hundreds of meters across the city. Initially believing Metal Bat got defeated by Elder Centipede, Garou decides to go after Watchdog Man. However, Metal Bat soon gets up and begins heading back to fight Elder Centipede. This causes Garou to attack Metal Bat.
At the Hero Association, the staff members are considering how to handle the monster. Just as Mohican and Pineapple were cornered, Metal Knight arrives and draws the attention away from them. Bofoi asks them to leave as he tests his new weapons. However, as the two heroes leave, the two heroes encounter three more monsters. These monsters also demand for the sponsors. In another part of town, Metal Bat and Garou are fighting it out.
Metal Bat and Garou continue to fight back and forth. Metal Bat launches toward Garou with an attack, but Garou manages to dodge it. Garou is surprised by Metal Bat's persistence despite Metal Bat's numerous injuries. However, Garou still believes that Metal Bat is at his limit. Much to Garou's surprise, Metal Bat's attack speed and damage suddenly increase drastically and Garou's attack are no longer able to faze him either.
Garou throws a manhole cover at Metal Bat, but Metal Bat hits it back with his bat. However, Garou already managed to reach Metal Bat by the time Metal Bat followed through. Metal Bat tries the take the offensive, but none of his attacks connect. Garou continues to mock Metal Bat, asking him if he's going to persist until he dies. Metal Bat retorts by saying he'll fight until he wins and proceeds to initiate a killing move. Unfortunately, Garou manages to repel the attack and launch a blow to Metal Bat's chest, leaving Metal Bat laying on the ground. Abruptly, someone shouts, "Big Brother!".
Metal Bat is about to land an attack on Garou, but stops when he hears his sister's voice. Garou then hits Metal Bat to the ground. Before the two could clash again, Zenko, Metal Bat's sister, manages to get in between them. She tells Garou the fight is over because Metal Bat promised to not fight in front of her. Garou respects their promise and leaves to find Watchdog Man. While Garou is leaving, monsters discuss how they could use him to their advantage.
Metal Bat and Zenko discuss how Zenko found Metal Bat. Before Zenko could finish explaining, Metal Bat remembers that Elder Centipede is still on the loose. Metal Bat tries to make his way towards the monster, while his sister tries desperately to stop him. Eventually, she gets frustrated and smacks Metal Bat on the back of his head, causing him to pass out, having already endured heavy injuries from both the Centipede and Garou. Phoenix Man realizes that this is the best opportunity to attack Metal Bat, but Sludge Jellyfish was already ways ahead of him. Sludge Jellyfish emerges from the sewers and thought aloud that he plans to kidnap Metal Bat's sister. Suddenly, Garou appears behind the monster and launches a deadly attack. Garou tells the monster that he hates being observed. Phoenix Man joins in on the conversation and attempts to invite Garou into the Monster Association. Unfortunately, Garou rudely declines by ripping up the invitation card and tells them to get lost. Sludge Jellyfish felt very offended by this act, but decided to not become aggressive. Phoenix Man laughs off Garou's behavior and tells him that he will overlook this act. Before leaving, Phoenix Man states that if Garou continues hero hunting they will definitely meet again, while Sludge Jellyfish simply remarks that he will not forget that Garou attacked him. After the monsters' departure, Garou simply says, "Disgusting". Pineapple and Mohican are frantically fighting against Rhino Wrestler, but to no avail. Rhino Wrestler is utterly bored by the heroes' pathetic attacks and decides to rate their attacks.
Rhino Wrestler boasts about his training towards his opponents and expresses his utter disappointment in the heroes that he is facing. Phoenix Man alerts Rhino Wrestler that it is time to leave and to take the hostages. In addition, he reminds Rhino Wrestler that today is not the "main event," so they can't do as they please. Finally, Phoenix Man tells Rhino Wrestler to only take the son. Mohican and Pineapple make a final desperate attempt to stop Rhino Wrestler, but fail miserably as Rhino Wrestler is able to easily charge through them. Afterwards, Phoenix Man alerts Elder Centipede that they have gotten what they came for. Elder Centipede then grabs Phoenix Man and Rhino Wrestler and leaves in the hole he created earlier. Metal Knight's robot quickly grabs on to Elder Centipede while Elder Centipede is leaving. In W-City, Heavy Kong has been struggling against Marshall Gorilla for 15 minutes. In D-City, Lightning Genji is fighting against Electric Catfish Man and Maiko Plasma. Meanwhile, many of the other cities are all simultaneously attacked by monsters ranked Demon and above. The opening ceremony for martial arts competition has finally started and Saitama is finally ready. Genos is waiting in the crowds to get into the C-City Super Stadium.
The Super Fight Announcer introduces all of the martial arts contestants in the tournament to the audience. Bakuzan desires to beat and possibly kill Suiryu. However, Suiryu only desires to fight the previous tournament's winner, Garou. Meanwhile, Garou has finally reached the Watchdog Plaza and is planning to fight Watchdog Man. Saitama converses with Sour Face when Zakos appears and starts questioning Saitama. Sour Face ends up answering some of Zakos questions. Zakos then reveals that Bang was supposed to be one of the judges and starts mocking the martial arts master. Sour Face starts to feel very insulted, but felt even angrier when "Charanko" did not seem angry at Zakos' comments. Saitama replies that he was not invested in the conversation and is only looking forward to fighting Zakos, but notes that Zakos doesn't seem strong. Bang and Bomb continue their search for Garou. Bomb notices that one of their marked A-Class heroes is being attacked and the two martial artist rush to scene. Smile Man is struggling against Fist Fight Djinn. Fist Fight Djinn boasts about his power before fighting Bang, but before he could finish talking, Bang unleashes his anger through a barrage of attacks, breaking every bone in the monster's body. He tells Bomb to continue to search for Garou before Garou becomes a monster.
Lin Lin and Lightning Max are about to fight at the tournament, while Darkness Blade, Dynamite Man, Saturn Man, and Pandaman are fighting Do-S. Crossbow S manages to bring three of the heroes under her control and command them to fight the Dynamite Man. Before they can deal too much damage,The Blizzard Group subsequently arrives, knocking out Darkness Blade and prepares to fight Do-S.
Do-S is about to attack the Blizzard Group, but Fubuki manages to stop it before it hit them. The two engage in banter before initiating their fight. At the tournament, Lightning Max manages to beat Lin Lin. Sour Face explains to Saitama (disguised as Charanko) what is a "reversed seed", and inadvertently Saitama then provokes Zakos. At W-City , Marshall Gorilla has defeated Heavy Kong. Lightning Genji continues his fight with Electric Catfish Man in D-City .
In D-City, Lightning Genji is pushed back by the two mysterious beings he is fighting, and while trying to strategically retreat and get help he is stopped, and sucker-punched into a nearby vending machine. Meanwhile in I-City, Hundred-Eyes Octopus is devouring a building when he is attacked by 3 heroes (Death Gatling, Butterfly DX and Bone) who unsuccessfully try to hit his "Blind Spot", they are then shortly defeated. In Y-City, Eyesight continues to wreck havoc by paralyzing all opposing heroes. Due to all of this, the Hero Association HQ is in disarray. In V-City, Pureblood claims that the Monster Association has made a miscalculation, saying that they have underestimated themselves, and overestimated the humans. Back at the tournament, Saitama has beaten Zakos with a single slap, much to Suiryu's attention.
The audience is excited as Suiryu enters the stage. Lightning Max tries picturing Suiryu as the Sea King so that he can overcome his real goal. Lightning Max tells Suiryu that Suiryu's strength is minuscule compared to the Sea King's. When the match begins, Lightning Max charges at Suiryu.
Lightning Max shows off his new move, but gets easily outmaneuvered by Suiryu. Suiryu proceeds to kick Lightning Max to the edge of the ring, knocking Max out. Everyone, except Saitama and Bakuzan, is impressed by Suiryu's performance. Suiryu apologizes to Lightning Max for being too strong. The fight between Sneck and Benpatsu begins. The Super Fight staff members are contacted that monsters have appeared nearby. The staff decide to evacuate the tournament, but Bakuzan goes against that decision, stating that it would only cause chaos. In addition, he suggests that he will take care of any monster that come in. Genos receives several alerts about the monsters as well and decides to take care of them by himself.
Sneck rather easily defeats Benpatsu. Meanwhile, Genos defeats several monsters throughout C-City. Genos contacts the C-Branch of the Hero Association. The Hero Association staff inform Genos of seven monsters that have appeared in C-City and their locations. During the match between Volten and Bazuzu, Volten easily wins.
Genos continues to take out the monsters as the tournament continues. During the tournament, Gatlin beats Hamukichi, Dave beats Rosie, Choze beats Mentai, and Sour Face beats Jakumen. Genos eventually encounters Face Ripper before the monster is able to kill a civilian. Face Ripper manages to chip away parts of Genos's arm, but Genos ultimately catches the monster off guard and is able to land a fatal blow. Genos contacts the Hero Association for the location of the final monster in C-City; this leads him to an alley. He finds Awakened Cockroach and several beaten heroes there. Meanwhile, Saitama prepares to fight Bakuzan.
Bakuzan walks up to Saitama when the match begins, puzzled by Saitama's lack of movement. When Saitama asks Bakuzan for a taste of Bakuzan's martial arts, Bakuzan fully accepts. However, as Bakuzan is demonstrating his martial arts to Saitama, he accidentally shifts Saitama's wig, causing Saitama to panic and launch Bakuzan into the air. Everyone is shocked by the sudden attack. Suiryu is impressed by Saitama's display and states he will end his next match in one hit as well. Tareo is frightened by the monster reports from the news, especially by the fact that the hero patrolling his city, Lightning Genji is defeated. At the Hero Association Headquarters in A-City, the staff discuss how to handle the situation and are incredibly anxious about not having enough heroes. Meanwhile, Awakened Cockroach and Genos continue to duke it out, wrecking havoc across C-City.
Genos and Awakened Cockroach continue to fight, but Awakened Cockroach has the upper hand. Genos decides to use instant adhesive to trap the monster. However before Genos could kill the monster, Awakened Cockroach sacrificed his feet to get away. Furthermore, before Genos could make up his mind about returning to the stadium, another being rushes to Genos. Meanwhile, Fubuki is struggling against Do-S. All of Fubuki's subordinates have turned into love slaves. While Fubuki tries to hold off Do-S's love slaves, Do-S's whip eventually manages to pierce through Fubuki's telekinesis and hit Fubuki.
Do-S manages to hit an injured Fubuki multiple times. Believing that she has Fubuki's mind under her control, Do-S approaches Fubuki and tells the hero about her plans to lure Tatsumaki out. Enraged, Fubuki sends Do-S flying back. Before Do-S could get a hold of the situation, Fubuki uses Hell Storm, which slightly injures Do-S. As it turns out Fubuki did not succumb to the monster's mind control. Do-S changes her plans and decides to kill Fubuki instead of using the hero to lure Tatsumaki out. Fubuki tells the monster that her sister would come anyway.
Tatsumaki causes an explosion in the city where Do-S and Fubuki are fighting. Do-S realizes the mistake she has made and immediately tries to make an escape plan. A monster falls in front of Do-S asking for help and warns her of Tatsumaki. Tatsumaki finally arrives and immediately tell Fubuki to go home and that she will handle the rest. Do-S orders her love slaves to attack Tatsumaki as a distraction as she escapes. Tatsumaki immobilizes all of the love slaves and tells Fubuki that they will only get in her way and to not call them her allies. She then takes off to find the rest of the monsters.