On the second school day of middle school, Saitama reads a health and physical education manual. He does not hear the talk about the two third-year bullies who beat up a freshman who called himself "The Bicycle Commuter" the day before.
After school on a rainy day, Saitama watches the news about an ongoing monster incident in Z-City and the increasing outbreak of monsters in the last decade. Saitama drifts off to sleep and forgets to do his homework. The next day, his homeroom teacher calls him to the teacher's room to rebuke him.
On the way to the teacher's room, he is confronted by the third-year bullies who had bullied the Bicycle Commuter. They demand his wallet, but Saitama tells them he doesn't have one and prepares to fight them instead. However, Saitama is too weak to defend himself and the bullies steal his 200 yen. Suddenly, Piggy Bancon rams one of the bullies and demands money from them. Saitama hears that one of the bully's reason for threatening the freshmen to steal their money was to pay for his little brother's lunches. Saitama chases after the monster to get the money back but the monster knocks him into a wall. After the police and special unit forces defeat the monster, Saitama returns to school to see his homeroom teacher.
The teacher scolds Saitama for his behavior. On his way home, Saitama thinks about how unfit he is for society.
Adulthood, First Hero Act
Three years before the start of the storyline, Saitama was an unemployed man on a job hunt. Before becoming unemployed, Saitama was working part-time at a convenience store. On one occasion, a robber was entering the convenience store. Despite the man pointing a knife at Saitama, all Saitama did was wonder where the barcode was, believing that the knife was one of the merchandise.
One day, after yet another failed interview, a dejected Saitama encounters Crablante on the street. Crablante notices Saitama's lifeless eyes and spares his life. He tells Saitama that the prey he is after is a child with a cleft chin.
As he walks on, Saitama spots the child Crablante mentioned. However, his nihilistic attitude takes over and he decides to not intervene in the matter. Suddenly, Crablante appears behind the child and attacks him, but Saitama impulsively saves the kid, which surprises himself. He urges the child to run away and demands to know why Crablante wants the boy dead. While Crablante explains the prank the boy pulled on him, Saitama chuckles and notes aloud how the monster resembles a creature from a children's cartoon he watched as a kid. This enrages Crablante, who pummels Saitama even after the latter resolves to live out his childhood dream of being a superhero by fighting back. Saitama then lassos one of Crablante's eyestalks with the loop of his tie and tears it out.
Resolving after this encounter to become a mighty superhero, Saitama started a daily training schedule which consisted of 100 push-ups, 100 sit-ups and 100 squats along with running 10 km every single day. He ate three meals a day, but only a banana as breakfast and also didn't use the air conditioner to strengthen his mental resistance. These daily activities were extremely tough and caused his body excruciating pain, muscle aches, and vomiting blood. However, Saitama did not give up and continued his training day after day.
Personification of A Light Pull Cord Attack
On Saitama's 300th day of training, his body had already felt the effects of working out too much. However, Saitama has shown signs of improvement, such as wrecking a car after saving a boy from an accident. At that time, Personification Of A Light Pull Cord attacked the streets, looking for an opponent that would satisfy him.
The monster punches cars and buildings as he keeps searching. To test the fruits of his labor, Saitama challenged the monster but was sent flying after a single punch. Filled with determination to overcome his limits, the monster punches Saitama again and is knocked down. However, Saitama quickly got up and spat out a tooth that had been bothering him because of a cavity.
Saitama then defeated the monster with a single punch before moving on with his workout.
At some point in the first year and a half of Saitama's training, Octopus Claw Man attacked an unspecified group of people. Saitama arrived and defeated Octopus Claw Man, though he sustained multiple injuries from the fight. After the fight, he consoled one flailing civilian who had suffered three scratches above his left eye from the mysterious being. When questioned about his injuries, Saitama shrugged it off, simply smiling at the thought that there was a special sale that day.
Magicicada Nymph Attack
Some time between when Saitama started training and started to lose his hair, Z-City experienced a mysterious being attack by the 170,000-Year Magicicada Nymph, prompting the citizenry to evacuate to the state-of-the-art Shelter Nr. 7. The three low-ranking heroes sent to defeat the Magicicada Nymph were defeated, but survived and managed to find some straggling evacuees on their way back to the shelter, among them being Saitama.
When Saitama discovered that he had been led to a shelter, he became upset, stating that he thought that following the heroes would lead him to the mysterious being. Saitama attempts to leave so he can find the monster but is restrained by the citizens, thinking he has become suicidal. The guard attempts to explain that the doors cannot be opened while the disaster is still ongoing, but reassure the public that the shelter can withstand any sort of attack. While she praises the structure's perfection, Saitama confronts her again to ask where the bathroom is, only for her to reply that the 'perfect' shelter was nevertheless designed and built without bathrooms.
Saitama slowly becomes more and more distressed, as he doesn't know if his bladder can hold until the situation ends. After overhearing that two A-Class heroes were defeated by the beast and that it will take three hours for a Hero Association squadron to arrive, Saitama can't take it anymore. He walks to a wall of the shelter and breaks a hole in it with a single punch before the stunned onlookers, and runs off stating that he's going to the convenience store. Just as he is about to reach the store to use the bathroom, the 170,000-Year Magicicada Nymph appears in front of him, which he promptly kills.
One and a half years after he started training, he had lost his hair and became strong. He continued his training for another year and a half before starting his superhero career.
Saitama appears at the scene just in time to save a young girl from Vaccine Man. The monster asks who Saitama is. Saitama replies that he is "just a guy who's a hero for fun". After reluctantly listening to the monster's angry monologue and watching its transformation, Saitama kills it with a single punch. After this, he screams out in frustration at another easy victory.
Sometime after, Saitama hears about a Demon-level disaster emergency stemming from the destruction of D-City by the The Brain and Brawn Brothers. Saitama appears on the monstrous Marugori's shoulder and tells him to put some pants on. Fukegao, Marugori's brother, who is on his other shoulder, orders his brother to swat Saitama. However, Marugori absentmindedly swats the wrong shoulder, instantly killing his brother. Enraged, Marugori grabs Saitama, throws him to the ground, and assaults him with a flurry of punches, leaving a large hole in the ground. Saitama jumps out of the hole and punches Marugori to the ground with a single punch. As Marugori topples over, Saitama states that having an overwhelming power is boring. Unfortunately, Saitama's blow causes Marugori to fall on top of B-City and destroy it.
Saitama has a dream where the Subterranean People attack him and give him an exhilarating fight. Saitama wakes up to the sound of the real Subterranean People. Saitama kills the leader instantly and his people retreat.
While Saitama laments his emotionless life, a mosquito land on his hand. After unsuccessfully swatting at it, it flies off and leaves Saitama enraged. Saitama then sees a news report about a mosquito swarm headed toward his city.
Saitama pursues the mosquito he had been trying to kill and encounters Genos fighting Mosquito Girl. At that moment, Mosquito Girl finishes her blood-fueled evolution and sends her mosquitoes crashing down on Saitama and Genos. Genos incinerates the swarm, unintentionally burning Saitama's clothes off in the process.
The newly empowered Mosquito Girl starts attacking Genos and tearing him apart with her claws. Just as Genos is about to resort to self-destructing, Saitama slaps Mosquito Girl, sending her flying through a nearby building and into the sky. Dusting off his hands, Saitama states that he hates mosquitoes. After witnessing Saitama's incredible power, Genos asks Saitama to make him his apprentice.
At Saitama's apartment, Genos gives a long explanation of his past and motives, but Saitama is completely uninterested. Nevertheless, Saitama agrees to take Genos in when Genos explains that he simply wants to become as strong as Saitama.
Meanwhile, Dr. Genus of the House of Evolution sends his creations to retrieve Saitama as a test subject after seeing him defeat Mosquito Girl. Kamakyuri arrives at Saitama's apartment first, crashing through the ceiling, but Saitama punches his head off. Saitama jumps outside and buries Frog Man and Slugerous in the ground. Ground Dragon grabs Saitama's legs and pulls his body into the ground, leaving only his head above the ground. Genos rushes Saitama's aid, but is intercepted by Armored Gorilla. Beast King then approaches Saitama.
Saitama starts to doze off, which angers Beast King. The creature threatens Saitama, who effortlessly steps out of the ground, much to the surprise of Ground Dragon. Beast King then attacks Saitama, killing Frog Man and Slugerous in the process, but Saitama dodges his attacks. Saitama uses Consecutive Normal Punches and obliterates the monster. The terrified Ground Dragon tries to flee underground, but Saitama digs underground and punches the monster out. When Saitama gets back to the surface, he finds that Genos has defeated Armored Gorilla, and is interrogating him. After Saitama shows Armored Gorilla the remains of Beast King, Armored Gorilla tells them all they want to know.
Roughly four hours later, Saitama and Genos climb a forest path and arrive at the House of Evolution headquarters. Wasting no time, Genos destroys the above-ground portion of the base with an energy blast, surprising Saitama slightly with his ruthlessness. In the rubble, they find a metal door which leads to the underground facility. As they enter the subterranean portion of the lair, they hear Carnage Kabuto bounding down the corridor. The monster slams Genos into the wall and challenges Saitama to a fight. Saitama accepts the challenge.
As the two are about to fight, Genos re-appears and attempts to fight Carnage Kabuto, but is beaten down again. Carnage Kabuto comments on how he can feel that Saitama is really strong, while Saitama tells him not to disappoint him, as he expects Carnage Kabuto to be the strongest being of the House of Evolution.
Moving with tremendous speed, Carnage Kabuto moves behind Saitama. Just as he is about to strike, he leaps backward. He senses that if he had attacked Saitama at that moment, he would have been killed. He explodes with rage and fear, and asks Saitama how he got so strong. Saitama agrees to tell everybody around him and explains that he got his strength by training his body. His regimen consisted of 100 sit-ups, 100 push-ups, 100 squats, and a ten-kilometer run every single day. Genos is outraged, stating that Saitama's strength would be totally impossible to achieve with that level of routine strength training.
Annoyed by Saitama's apparent lie, Carnage Kabuto enters Carnage Mode and states that he will rampage for a week until the next Saturday. Carnage Kabuto then begins to pummel Saitama, sending him flying around the room. While this is going on, Saitama comes to the horrifying realization that if Carnage Mode lasts for a whole week ending on a Saturday, then the current day is Saturday and he missed the special sale. Overcome with despair, he cries out and obliterates Carnage Kabuto with one punch. Genos informs him that they still have some time if they hurry to the sale.
Saitama is first seen waking up frantically from a dream involving someone pointing a snotty finger at him. Realizing it was just a dream, he turns on the news and finds out that the criminal Hammerhead and his terrorist organization known as the Paradisers, consisting entirely of bald, dangerous-looking men have arrived and started wreaking havoc. The news warns everyone to avoid any bald men with a dangerous aura. This angers Saitama who states that this group will ruin his image, as everyone will mistake him for a villain. He resolves to destroy the Paradisers to protect his image. Saitama heads out to search for the villains, and on his way, many people end up mistaking him for a member of the Paradisers.
On his search for the Paradisers, Saitama finds himself lost in a forest. Trying to find a path out, he is halted by Hammerhead. Hammerhead mistakes Saitama for someone wanting to join up with the Paradisers, but Saitama tells him that he actually came to destroy them. Hammerhead swiftly attacks Saitama with a vicious punch, but Saitama is unfazed and unimpressed. Enraged, Hammerhead charges up to full power and executes his Windmill Attack. Upon seeing this, Saitama notices it looks much like an "attack" he used to perform as a kid and wonders if Hammerhead is similar to him. He then stops the attack with little effort and shatters Hammerhead's battle suit with a quick punch. After making him promise to never do bad things again, Saitama allows Hammerhead to flee.
Shortly after, a powerful ninja, Speed-o'-Sound Sonic, arrives demanding to know where Hammerhead has gone. Saitama points in the direction that Hammerhead fled in. Sonic then attacks Saitama, mistaking him for a member of the Paradisers, with a kunai thrown at lightning-fast speed. However, Saitama effortlessly catches both the kunai and Sonic's subsequent attack with a sword and then proceeds to break the sword in half. Saitama then frantically explains that he is not a member of the Paradisers, and asks Sonic whether or not he recognizes him as the man who has saved the world many times. When Sonic denies knowing him, Saitama becomes severely disheartened. Sonic again proceeds to attack Saitama, stating that the real problem is that Saitama was able to see two of Sonic's attacks, and that his pride cannot allow for Saitama to live. Upon hearing this, Saitama accuses Sonic of being a liar, stating that Sonic just wants to test his attacks on him, indicated by the "childlike smile" on Sonic's face.
After Sonic jumps around for quite some time, Saitama intercepts him and asks if he can go home now. Surprised, Sonic retaliates with a Wind Blade Kick. Saitama attempts to interrupt Sonic's attack by placing his fist directly in the path of Sonic's groin. However, he accidentally moves his fist too far and taps Sonic's groin. Clearly in pain, Sonic swears that he will train day and night for their rematch and then flees.
Later, Saitama is at his apartment going over the day's events with Genos. Saitama asks Genos to leave, stating that he is in shock due to a certain event that occurred that day. Genos, worried about anything that might shock Saitama, asks what it was, and Saitama explains that he cannot believe that Sonic had no idea who he was despite all of his previous exploits. Genos then asks if Saitama was a registered superhero, to which Saitama replies that he is not. Genos goes on to explain that anyone who hasn't registered with the Hero Association will never be recognized for their feats. Saitama resolves to become a licensed hero so he can achieve the fame he deserves. He asks Genos to register with him in exchange for formally accepting the latter as his disciple.
Saitama arrives at the 6th Official Superhero Certification Exam Center, and begins a series of physical tests. Saitama does so well on the physical tests that he awes the examiners and disheartens the up and coming heroes from taking the tests altogether.
Later, in the waiting room, Saitama meets with Genos, and the two discuss the easiness of the hero qualification tests, and state that there is no way they didn't pass. When the results of the tests arrive, it is revealed that Saitama barely passed, having achieved a score of 71 when the passing is 70; and received the C-Class hero designation. Despite this, Saitama achieved a perfect score in every physical test and broke every record of the Hero Association, and the only reason his score was so low was that he did poorly on the written test.
Later, during a lecture from an A-Class hero Sneck, Saitama is chewing bubble gum, seemingly bored. This angers Sneck and, along with hearing the news that Saitama could quickly surpass him, causes Sneck to ambush Saitama. However, he is quickly defeated.
Sometime later, Genos requests a sparring match with Saitama. Saitama, having earlier agreed to take Genos as his disciple officially, under the condition that Genos registers as a hero as well, accepts his challenge. The battle begins with Genos firing a massive energy attack which Saitama dodges with ease. Genos proceeds to attack Saitama physically, but eventually discovers he was chasing Saitama's afterimage the whole time. After an extremely close-range energy attack in which Genos believes he finally landed a blow on Saitama, Saitama, having dodged the attack, pokes Genos' face and declares himself the victor. Genos stops to reminds him that the match cannot end until one of them is unable to continue. Upon hearing this, Saitama appears in front of Genos, and delivers a Death Punch, which stops inches before hitting Genos' face. Though unharmed, the landscape behind Genos is obliterated. Saitama and Genos then return home.
After the sparring match, they head out to a shop, where they had an eating contest. While Genos had no problem eating, Saitama nearly passed out. The A-Class hero Sweet Mask comes, and asks Genos to speak with him outside, with Saitama warning Genos about rookie crushing.
Five days later, Saitama is seen lounging around his house reading a magazine. He notices Genos, carrying a huge backpack full of contents unknown, who then requests to live with him. At first he declines, but after Genos tells him that he will pay him the rent, Saitama allows Genos to stay with him.
Genos later informs Saitama that all C-Class heroes who are inactive for a week are removed from the official registry. Saitama, realizing he only has two days remaining, sets out to find a villain, only to discover that Z-City is completely peaceful. Saitama decides that he will check again the next day and returns home. Upon discovering that Z-City is peaceful for the second day in a row, he becomes greatly distressed. All of a sudden, a kunai is thrown at Saitama. Saitama catches it, and discovers that his would-be assailant is Speed-o'-Sound Sonic.
Saitama tells Sonic that he is busy, and begins to walk away, but Sonic rushes to intercept him. Frustrated, Saitama bites Sonic's sword, shattering it in the blink of an eye. Saitama then threatens Sonic, that if he gets in his way again, he will punch him. At this moment a woman from the crowd observes Saitama and states that he is a 'suspicious person'. Saitama, thinking that the woman was referring to Sonic, begins to lecture Sonic for being so violent. Then, a C-Class hero, named Tanktop Tiger, explains that the woman was referring to him. Saitama says that he is also a registered hero, but Tanktop Tiger states that he has no idea who Saitama is, and thinks that he should leave as he is ruining the reputation of other heroes. Saitama becomes increasingly annoyed, but before he has a chance to attack, Sonic launches a surprise assault on Tanktop Tiger, who is defeated instantly.
Sonic begins to wreak havoc on the surrounding civilians. During this chaos, Saitama saves a small boy's life by effortlessly moving a tree in place to intercept a falling car that would have killed the boy. Saitama, angered both by the fact that he can't find a bad guy to fight, and that civilians are in danger, realizes that Sonic is now considered a bad guy and decides to retaliate. Saitama appears behind Sonic and dispatches him with a single swift chop. By defeating Sonic, he has saved himself from being removed as a registered hero.
Saitama, apparently returning home from shopping, happens upon a scene where Kombu Infinity had just defeated two A-Class heroes in battle. Upon seeing the monster, Saitama remembers that he forgot to get kombu and notices that the monster appears to be made of it. Later that day, Saitama is seen cooking kombu that was taken directly from the monster's body, leaving it totally naked. Genos states that Saitama wanted to eat kombu to see if it could make his hair grow back.
Saitama and Genos are relaxing in their apartment when Genos tells Saitama that he's been promoted from C-Class rank 388 to rank 342, and while he hasn't been raised from S-Class rank 17, he's been ranked 6th in popularity. Genos then gets a call from the Hero Association and heads out.
Later, after Genos fails to destroy the meteor heading towards the Earth, Saitama shows up and asks Bang to take care of Genos. He then launches himself at the meteor and punches his way through it, causing it to break apart. Unfortunately, the pieces of the meteor then rain down on Z-City. Saitama lands, and then walks off, concluding that the situation is taken care of.
Three days later, Saitama and Genos are relaxing in their apartment, watching a news report on how the meteor fragments destroyed many buildings and businesses in the city. After learning that his rank had jumped up from C-Class rank 342 to rank 5, Saitama gets excited and decides to go out for a walk around town. During his walk, he gets called out by Tanktop Tiger, but Saitama doesn't remember who he is. Tanktop Tiger then declares that Saitama is a liar; that there is no way he would be able to destroy a meteor on his own, and that he merely took credit of the S-Class heroes' work. Saitama starts to defend himself but is cut-off by Tanktop Tiger who calls out for his big brother, who jumps in and introduces himself as Tanktop Black Hole.
Tanktop Black Hole claims that he has a perfect punishment for a "lying cheater" like Saitama. He then, in a rather loud voice, starts accusing Saitama of destroying the town. The commotion starts to attract citizens who begin to gather around the scene. Tanktop Black Hole continues to accuse Saitama of destroying the town on purpose and slowly, the crowd begins to turn on Saitama, shouting out threats and accusations along with Tanktop Black Hole. Tanktop Black Hole then accuses Saitama of wanting to destroy the citizens, just as he "destroyed" the town, and then challenges him to a fight. Tanktop Tiger then rushes forward to attack Saitama, but gets easily knocked away into a pile of rubble, much to Tanktop Black Hole's surprise. Tanktop Black Hole then jumps in and tries to crush Saitama with his grip. Saitama intercepts him and locks hands with Tanktop Black Hole and squeezes, causing him to fall to his knees in pain, and apologize for lying. To his surprise, however, Saitama tells him that he wasn't lying.Saitama then shouts to all the citizens that he did destroy the meteor and that if anyone has a problem with him they should say it to his face. Some citizens move to accuse him of damage done to their property, but Saitama quickly shouts them down, telling them to blame it on the meteor, and that he's not doing hero work because he wants to be admired by them, but because it is something he wants to do, leaving his accusers stunned in silence.
On his way home, Saitama comes across a Seafolk about to attack a city, so he defeats it quickly. Sometime later, Saitama is relaxing as Genos does dishes and explains that Saitama has advanced to the second rank of C-Class. He goes on to explain that once Saitama becomes rank 1, he can get promoted to B-Class. Genos then starts talking about how the top-ranking C-Class hero hasn't left his position for around half a year, which apparently is no match for the top-ranking B-Class hero. Before Genos can finish talking though, he gets a call about an attack on J-City by more Seafolk. After seeing a news report on the incident, they decide to head out to help.
Sometime between them leaving, and them getting there, Saitama and Genos get separated. During his search for the Deep Sea King, Saitama finds Mumen Rider's cell phone lying in the street. Upon picking it up, the man on the other end of the line requests to know who he is speaking to and, despite Saitama only being listed as a C-Class hero, decides to disclose the location of the Deep Sea King, apparently to finally determine just how strong Saitama is.
Later, Saitama arrives at the shelter just in time to witness Mumen Rider's defeat at the hands of the Deep Sea King. He catches Mumen Rider's unconscious body, and tells him he fought well. Saitama then observes the scene, and is surprised to find that Genos is still alive despite his grievous injuries. After remarking that he will quickly dispatch the Deep Sea King, Saitama is attacked by the monster. However, he is unscathed by its attack.
Deep Sea King declares his surprise that Saitama did not fall from his punch, but Saitama remarks that the monster's punch was simply too weak to hurt him. Meanwhile, the spectators talk among themselves, telling each other that their situation has not changed at all with only a C-Class rank 2 hero arriving. Deep Sea King starts to tell Saitama that he, as the ruler of mother sea, stands at the very top of the pyramid of all living organisms on Earth. Saitama interrupts Deep Sea King and tells him to hurry up and fight. Deep Sea King then quickly attempts to punch Saitama, only for Saitama to punch a hole in his body. As Deep Sea King falls, Genos is seen smiling, and all the spectators stare on in disbelief.
Standing triumphantly over the body of the monster, Saitama overhears the crowd of onlookers, starting to question the usefulness of the rest of the heroes who battled the monster. Not wanting the heroes' good reputation to be tarnished, Saitama remarks loudly that he got off lucky, and that, if the other heroes hadn't weakened Deep Sea King beforehand, he wouldn't have stood a chance. To further the credibility of his ploy, Saitama plays on the rumors of his underhanded nature by stating that, because he is the one who dealt the finishing blow, he'll get all of the credit for the victory, regardless of the other heroes' valiant efforts. Saitama's plan proves successful, and the people's faith in the other heroes is restored. Saitama, on the other hand, grows more hated in the eyes of the citizens. Internally, Saitama reflects on how dull the battle with Deep Sea King turned out to be.
Sometime after the battle with Deep Sea King, Saitama and Genos receive a box via airdrop from the Hero Association, containing several letters addressed to the heroes themselves. Upon opening the five letters that were addressed to him, Saitama discovers that the first three contain nothing but hateful words accusing him of cowardice and cheating, which angered Genos greatly, but were disregarded by Saitama. The fourth letter contained a simple thank you message from an anonymous sender. The fifth letter turned out to be a letter directly from the Hero Association itself, notifying Saitama of his promotion to C-Class rank 1, and inviting him to the Hero Association Headquarters in Z-City.
Upon arrival, Saitama requests to know why he was summoned to the headquarters and suspects that they called him there to reprimand him for his actions. His hosts, however, insist that the circumstances for which he was invited are quite the contrary and they congratulate him on reaching C-Class rank 1. They then go on to inquire as to whether or not Saitama will move up to B-Class or remain in C-Class. Saitama expresses his apathy on the subject but then goes on to state that he'd rather be B-Class, since he would no longer have to report his weekly activities to the Hero Association. He also internally reflects that he can't remain in C-Class forever, especially considering that Genos is already in S-Class. Other officials of the Association watching from a separate room question even the legitimacy of his exam results, to which one suggests that they allow him into B-Class to test that legitimacy: should he hold his own, his power would be unmistakable, otherwise he will be broken by the factions in B-Class, in particular the Blizzard Group. Finally, they consult Sweet Mask for the verdict. Sweet Mask, finding neither significance in promotions from C-Class to B-Class, nor anything noteworthy in Saitama's impression, allows it.
Later on, Saitama is walking home, examining the official document declaring him a B-Class hero, when a delightful smell from a small oden shop draws him inside. Upon entering, Saitama orders an assorted oden and takes a seat at the counter where he is asked by another patron in the shop if he will have anything to drink with his oden. The patron then states that, if Saitama won't order a drink, then he will treat him to one. Upon observing this stranger, Saitama discovers it is none other than a bruised and battered Mumen Rider. Saitama questions why Mumen Rider would want to buy him a drink, to which Mumen Rider states that, if for nothing else, it would be to celebrate Saitama's promotion to B-Class and also reveals himself to be the sender of the "Thank You" letter that Saitama had received. Upon finally recognizing the man as Mumen Rider, who he saved from Deep Sea King, Saitama accepts his offer, and orders a mozuku.
Some time afterward, Saitama would rank up from B-Class rank 101 to rank 63.
Saitama and Genos are watching the martial artist hero, Bang, demonstrate one of his techniques to the duo. Upon being asked to attempt the technique, the pair express their disinterest in a non-destructive technique, eliciting an outburst from Bang's only disciple Charanko. After being questioned on the whereabouts of the rest of his students, Bang explains that a long time ago one of his students went out of control and defeated a good handful of them, causing all of them to leave the dojo; subsequently forcing Bang to take it upon himself to take him down. Shortly after, a member of the Hero Association arrives and declares that all S-Class heroes are to report to HQ immediately to address a major crisis. Genos states that, since all S-Class are being convened, they might need Saitama's power, so Saitama accompanies them to HQ.
The first S-Class hero to interact with Saitama is S-Class rank 4 Atomic Samurai, who even after hearing the praise of Saitama from Bang, refuses to shake Saitama's hand; stating that he will only acknowledge those in the S-Class. Saitama then hears a flurry of disapproving remarks at his presence at the meeting and looks over to discover the culprit is a very small girl who, to his surprise, happens to be the S-Class rank 2 Tatsumaki. Thinking she's just some cheeky kid, Saitama blatantly ignores her, and goes to sit down with the rest of the heroes, angering Tatsumaki, who continues to complain. As most of the S-Class heroes are conspiring with their own thoughts, Bang asks what they were called here for. Saitama then casually asks for some tea.
After having heard of the great calamity foretold by the renowned fortuneteller Shibabawa, Sitch unnervingly elaborates on how punishing the impact of the most recent prediction she had made before her death would be. He tells the assembled heroes that the prediction may come true at any time in the next half a year. Saitama could not help but simply muse that this disaster that has the Hero Association coordinator so on edge could just as well occur today or tomorrow for that matter. After Sitch asked him who he was, Saitama simply states how glad he is to have come along for the meeting.
Just as he was finished bemusing over the emergency meeting, the entire building complex shook with thunderous turbulence as though it had been hit by a massive tremor, while outside the complex numerous flying creatures led by the Sky King could be seen gathering around for an all-out assault on the surface world. However, the would-be incursion was soon dispatched by a UFO-like albatross the size of a major metropolitan area. Having already picked up on what had happened to the obliterated A-City outside the Hero Association's HQ, Saitama quickly leaps all the way to the rooftop to get a better view of the action before Genos could even erect a response out of him.
Upon seeing the giant spaceship, Saitama heads towards it, evading and deflecting cannon fire directed at him. As soon as he managed to reach it, Groribas gets in his way, but is defeated in a single punch. Saitama keeps searching inside while wrecking whatever and whoever got in his way. Geryuganshoop tries to beg him into leaving the spaceship to no avail. Saitama eventually reaches Boros' throne room entrance, the leader of the invading Dark Matter Thieves. Before Saitama can reach Boros, however, Geryuganshoop challenges him, only to be easily dispatched; Saitama stating that flinging rocks around using telekinesis was a waste of superpowers before flinging one through Geryuganshoop's head. Boros was amazed that he managed to defeat his strongest fighters as easily as he did and proceeded to take him on.
As the battle of the S-Class heroes and alien invaders began, Saitama's own battle with Boros was getting underway. After hearing why the aforementioned galactic warlord went on a tirade, shattering planets and razing civilizations, all due to insurmountable boredom out of being an unstoppable force looking for a worthy opponent to temper his might, Saitama expresses his disgust towards Boros' petty genocidal indulgence and whacks him. Doing so, however, inadvertently shatters his armor which acts as a restraining bolt on the intergalactic raiders own power. This somewhat surprises Saitama as this new opponent was one of the first individuals he has ever met to survive his one-hit kill blow. Soon metamorphically shifting into a more powerfully energized form, Boros begins releasing his unsealed inner power. As the two clash repeatedly, Boros compliments Saitama on having lasted this long against his might while the latter retorts that his adversary is equally impressive.
As the battle grows more and more intense, Boros begins taking the upper hand in the conflict against Saitama, knocking him around his vessel's throne room, eventually culminating in the two plowing through to the top of the ship. There, Saitama weathered some of Boros' strongest attacks, while only taking minimal damage in his assault. After having grown bored with Boros' constant boasting and flaunting of his regenerative capabilities, Saitama wonders aloud if he was finished due to his inability to fight seriously. Boros responds by unleashing his most powerful transformation yet, his "Meteoric Burst". Boros then unleashes a thunderous onslaught which began annihilating his own ship, subsequently kicking Saitama all the way to the moon. Saitama quickly realizes where he landed, catapulting himself from the moon's weaker orbit back to earth, landing meteorically upon his adversary's ship, causing it to jolt towards the ground upon upheaval due to the impact. Boros, now infuriated, furiously assaults Saitama, but Saitama simply counters with a devastating blow of his own, a simple punch that promptly eviscerated Boros, only for him to quickly regenerate his scattered self back together.
Initiating his final measure, the dreaded Boros struck out at his worthy opponent with his planet-killing trump card Collapsing Star Roaring Cannon, intending to decimate Saitama and the earth's surface layer in one gigantic blast. However, Saitama, unfazed by this apocalyptic announcement, simply says he would counter with his own winning trump card; his Serious Series: Serious Punch, which not only deflected the genocide wave which obliterated Boros on the spot, but also parted the cloud cover for several thousand miles across the globe. While he lay dying, admitting he found the excitement he long sought after while making his way across the cosmos, Boros commented that he and Saitama fought to the bitter end with neither giving an inch with Saitama nodding in compliance. Boros says he knew full well that Saitama was still holding back the entire time they fought, disparaging at how powerful his better truly was with his last breaths, leaving Saitama to solemnly walk away from his fallen enemy in the collapsing fortress.
After finally making his way out of the ruined spaceship, Saitama meets with many other S-Class heroes such as Superalloy Darkshine, Tatsumaki and Atomic Samurai. After being asked how and why he was on the enemy ship, Genos comes rushing to the scene, concerned for his well being. After a brief conversation over who Saitama was fighting against, and how prophecies could have come to pass without his help, which Saitama writes off as untrue, Tatsumaki bursts into a fit of anger, interrupting them both. She denounces Saitama for what she perceives as interference in her battle, calling him names. With some coaxing from Saitama, Genos steps up and tells Tatsumaki off, seconds before being telekinetically thrown into some debris by her in outrage of being called a brat, only to be stopped seconds away from attacking Saitama by Bang, who admonishes her for her callous behavior as an S-Class hero.
Saitama and Genos are in M-City, where they detect King's presence thanks to Genos. Genos wonders why King is there. While they talked, a sudden commotion occurred, where the source is the robot G4, whose primary goal is to eliminate King in the name of The Organization. Though Saitama offered to help Genos fight G4, Genos declined in the hopes of making it to the top 10 of S-Class, so Saitama leaves the matter to Genos.
While King struggles to choose a name in a video game, Saitama enters King's residence. At first, King didn't notice Saitama at all, responding to him casually when Saitama recommends him a name. Once King finally notices Saitama, Saitama states that the window was open, despite it being on the 22nd floor.
Eventually, King remembered Saitama from the S-Class meeting and quickly changes the video game to an action game, claiming he got the wrong game by mistake. As Genos was fighting G4, King just played video games. However, Saitama suddenly starts questioning King's escape from the fight against the robot. As Saitama is going to exit, a giant bird-like monster appears, flying directly towards King's room. Lucky for King, Saitama stopped the monster in time by holding its beak. Saitama gives King the chance to fight the monster, but King is reluctant. Saitama then wonders if King attracted monsters, making King reminisce his past. It is then shown that King really was attracting monsters before, only to be stopped by a mysterious figure from time to time.
Because of his appearance at the scenes, people began to treat him as the hero, giving him the hero name "King". As King was driven to the point where he teared up, silence entered the room, making him think the monster ate Saitama. However, Saitama begins to notice that all the rumors about King were mere lies, but that didn't make him angry. King concludes that Saitama beat the monster, and also learns that it was Saitama who saved him countless times, albeit Saitama still had hair at the time. King begins to apologize to Saitama and confesses that he stole the glory from Saitama's accomplishments. Still, Saitama urges King not to quit and just become strong for real. Saitama leaves, holding no grudges against King, still thinking how he wanted to play games with King.
Fubuki, along with Eyelashes and Mountain Ape, goes to Saitama's place to convince him into joining their hero group. However, Saitama's casual refusal urges them to take him down, but backfires, as Saitama easily knocks out both Eyelashes and Mountain Ape. She expresses her will to secure her position as the rank 1 in B-Class and attacks Saitama with a psychic barrage, but Saitama is unaffected by her ability. Saitama withstands all of her attacks and even patronizes her about being a hero. She asserts her will and continues to attack, this time with a box cutter, but is interrupted by the impact of Genos' attack on Speed-o'-Sound Sonic. Saitama quickly gets between Fubuki and Genos' attack, which would have probably killed her.
Wondering about Genos' presence, she is more surprised that the S-Class hero actually called himself the disciple of the B-Class Saitama. Genos recognizes her but misinterprets her position as being a failed attempt at taking down Saitama, when in actuality she was caught in his attack. Sonic then proceeds to attack Genos with exploding shurikens, but they do no damage. The two are on equal footing and eventually, Saitama attempts to stop them.
Upon observing Saitama's ability while battling Sonic, Fubuki found out that Saitama is too strong, which is far from the norm for his actual ranking. It is revealed that she has an inferiority complex due to her sister's own power. Due to this, she founded the Blizzard Group to surpass her sister, who is a lone wolf. Still, she reveals that she does not want to advance to A-Class, due to the A-Class heroes being overwhelmingly powerful, such as the Disciples of Atomic Samurai and Sweet Mask. However, she acknowledges that she can get to the upper ranks of A-Class.
In a final attempt to persuade Saitama into joining her faction, Fubuki belittles Saitama, saying he won't advance alone and that there are several other heroes out there that far stronger than he is. However, when King appears demanding Saitama return the video game he borrowed, Fubuki decides to follow him and be a part of his group, noting that the strong are attracted to Saitama, who does not discriminate on strength. Saitama is shortly after given the hero moniker "Caped Baldy" by the Hero Association.
Saitama is playing a video game with King, along with Fubuki and Genos, when he is visited by Charanko, who wanted to know why his master, Bang, expelled him all of a sudden. Genos tells Charanko that Bang expelled him to keep him safe, because Garou was actively hunting heroes. Saitama does not remember who Charanko is and has to be reminded by Genos that Charanko is Bang's one and only disciple.
Saitama visits the heroes at the hospital who were beaten by Garou, particularly Mumen Rider, Tanktop Master and Charanko, to give them some bananas as treats and to learn more about Garou. He first visits Mumen Rider and Tanktop Master, where he asks to know who exactly Garou is. Now knowing that Garou is a strong villain, he wishes to meet and battle him someday in person. After that, Saitama visits Charanko to learn more about martial arts, and who he could fight to learn more about them. Charanko offers him a ticket to observe martial arts at the tournament called the Super Fight that he was originally supposed to participate in, but couldn't due to his injuries. Saitama accepts the offer. However, Charanko advises him not to do something like disguising himself to cover his identity in the tournament. Enticed by the 3 million yen prize for first place, Saitama intends to achieve exactly that.
After Saitama finds a wig shop, he is sneak attacked by Garou. Garou, thinking that Saitama is after him, tries to hit him with a swift karate chop to the shoulder. However, Saitama is not only unaffected, but also fails to recognize his attacker. Annoyed at Garou for attacking him, Saitama counters Garou's attack by using a karate chop of his own, which knocks out Garou almost instantly, and then carries on shopping for a wig for his disguise. On the following day, Saitama prepares himself for the tournament by putting on the wig. Genos sees what Saitama is doing and, believing that Saitama is trying to make up for his lack of hair, decides to help his master by calling Dr. Kuseno, asking him for a hair transplant for Saitama. After getting the doctor to agree, he asks Saitama if he is free that day, at which point Saitama is finally able to explain that it is a disguise for the tournament, used to make himself look like Charanko. Saitama then asks Genos to join in to learn what martial arts are really about.
Saitama is in Charanko's waiting room looking over a list of the contestants of the tournament. He is then greeted by Sour Face. Sour Face discusses a tournament incident that happened in the past and his reasons for joining the tournament. Lastly, he talks about the day when Garou rampaged through the dojo. Saitama states that what Sour Face is doing is pitiful, and claims that he will be the one to put Garou down in the end, unaware that he had already beaten Garou before the tournament, which aggravates Sour Face.
After the tournament introductions, Saitama is talking with Sour Face backstage, 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 bothered by 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.
Saitama asks Sour Face what a reverse seed is after Max's and Lin Lin's match. Zakos tells Saitama they're reverse seeds, and Saitama inadvertently angers Zakos by calling him a weakling. In his fight against Zakos, Saitama single-handedly beats him, which surprised the audience and brought the attention of Suiryu.
During Max's fight with Suiryu, everyone is impressed except Saitama and Bakuzan. Saitama prepares to fight Bakuzan after Sour Face's match. As the match is starting, Saitama asks Bakuzan for a taste of Bakuzan's martial arts, which the martial artist 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. Bakuzan crashes out of the ring into the floor, headfirst.
Saitama goes on to face Sour Face and defeats him in a manner similar to Bakuzan. Even landing him in a spot next to where Bakuzan was.
Saitama is pitted against Choze in the semi-finals and defeats him, proceeding to the finals of the Super Fight, where he faces Suiryu. During the fight, Suiryu uses a strong kick that has enough force to knock off Saitama's wig. During the fight both express the struggle to find strong enough opponents, to which Saitama agrees and asks Suiryu to give him the true experience of martial arts, since he's starting to get tired of ending his fights with one punch. Suiryu agrees and asks for the same.
As their fight continues, Saitama manages to block some of Suiryu's kicks, until he is struck into the air and kicked back down, with Suiryu landing on his face. Saitama comes out unscathed, but struggles to keep his wig on while blocking and dodging. Saitama is then dared to punch back, but instead backs away. When Suiryu asks Saitama about his routine, Saitama accidentally lets it slip he beats monsters and tries to mend it by saying he wants to join the Hero Association, but is blown off by Suiryu. After listening to Suiryu's philosophy, Saitama's wig comes off when Suiryu kicks his head. Saitama replies back, telling Suiryu not to get any stronger if he wants to keep having fun, before throwing a punch, stopping before Suiryu's face.
After his wig came off, Saitama is disqualified and Suiryu is declared the winner. However, Suiryu still continues to attack him and doesn't hold back. Suiryu uses multiple barrages of many different attacks, but Saitama is completely unfazed. After tanking Suiryu's Void Sky Dragon Fist, Saitama concludes that martial arts are just about moving in a cool way. Saitama then tries to mimic Suiryu's moves, and accidentally launches Suiryu out of the ring into the crowd. However, Suiryu is still chosen as the winner of the tournament, due to Saitama breaking the rules. The referees then try to catch the running Saitama.
Saitama later returns to the arena after hearing Suiryu's voice calling for help. Saitama saves Sneck from Bakuzan, and commends Suiryu for holding his own against the monsters. He then proceeds to confront Bakuzan, telling Suiryu to leave the rest to him.
Suiryu is overwhelmed by Saitama's arrival. Bakuzan recognizes Saitama as the opponent who had defeated him in the tournament. The monster unleashes a flurry of blows on Saitama, who is completely unaffected. Saitama tries to recall Bakuzan, but fails to do so. The hero then punches Bakuzan, blowing off much of the latter's torso and killing him. Saitama then introduces himself to Suiryu.
Suiryu thanks Saitama and warns him of Gouketsu and the Monster Association's invasion. Saitama decides to go and fight Gouketsu. Suiryu tries to prevent him, but fails. Moments later, Saitama kills Gouketsu with one punch, sending Gouketsu's head flying into the arena right in front of Suiryu. Suiryu decides to become a hero after being inspired by Saitama. Suiryu then asks Saitama to accept him as a disciple, but Saitama flatly refuses.
Saitama immediately leaves in search of other monsters but is unable to find them. He finds out from the C-Class hero Water Gun that the monsters were attacking for 3-4 hours before retreating simultaneously. Saitama feels bad for being oblivious to such an emergency and reflects on himself and questions the Monster Association's actions. Recalling today's events, Saitama wonders if his boredom is the cause of him forgetting something very important. He feels disappointed that he didn't get to face Garou. Despite fighting the best of the best martial artists, Saitama gained nothing insightful. The hero returns home after killing a random monster.
On the way, Saitama meets King, who was on his way to buy manga. King and Saitama have a deep discussion on what it means to be a hero. Garou spots King and is about to attack when Saitama kicks him and sends him crashing into a wall. Both Saitama and King are unaware that it is Garou. Saitama continues hoping to meet the Hero Hunter who might give him a good fight.
Saitama is playing video games with King, and manages to put King on the ropes, but is still unable to defeat him, even with a two-finger handicap. On his way to take out the trash, Saitama is attacked by several monsters but he disposes of all of them without any trouble in a short amount of time. He begins to wonder if those monsters are looking for him. However, when he looks at the time, he then rushes to beat the garbage truck.
Saitama continues to play video games with King and as he is about to win, King easily turns the tides and defeats Saitama, much to his frustration. Saitama notices King's Emergency Transmitter has been beeping. King notes that there is a monster nearby, but informs Saitama that S-Class heroes are already at the scene. King then asks about Genos' whereabouts, to which Saitama states he doesn't know. Saitama is then informed about the Monster Association and decides to head over toward the monster, worrying about Genos' safety.
Saitama and King arrive just in time to witness Elder Centipede about to kill Bang, Bomb and Genos. King lures Elder Centipede in with promises of fighting Blast. When Elder Centipede is lured in, Saitama annihilates the gigantic beast with a Serious Punch. Genos, after witnessing Saitama's latest display of power, limps over to him, asking Saitama what it is he's lacking, to which Saitama simply replies "power", much to the exasperation of King.
Saitama brings the wounded heroes back to his apartment to rest and plays a monster fighting game with King. Fubuki arrives at the apartment and explains to the group the current state of alert of the Hero Association thanks to the Monster Association. Unfortunately, most of the group is still too badly injured after the fight against Garou and Elder Centipede. King predictably makes excuses and cops out.
Thus Saitama, growing increasingly annoyed with Garou, decides to put his costume back on and deal with him himself. He also plans on picking up cabbage while he's out.
During his trip to find Garou, Saitama eats at a restaurant where Garou also eats in at the same time, but he forgot to bring his wallet. As a result, he falls into a panic, unable to call Genos for help since Genos is still busy fixing his body. Suddenly, Fubuki comes to offer her help to find Garou in exchange for 70% of the credit. Furthermore, she also proposes to help him stand at the top 5 in B-Class as she still believes Saitama cares about his ranking. At the same time, what Fubuki doesn't know is that Saitama deliberately orders a large french fries dish to trick Fubuki into paying for his meal.
As Garou commits dine-and-dash in the restaurant, Saitama grabs the opportunity to run and capture him, leaving Fubuki stunned. When Saitama manages to catch up with Garou, he gives Garou a warning about eating-without-paying and then leaves the scene because he is grateful for Garou for getting him out of the same circumstance. However, this enrages Garou, as he thinks Saitama takes pity on him and tries to hit Saitama. Unfortunately for Garou, Saitama knocks out Garou for the third time and runs away without realizing he found and easily defeated the person he was looking for.
Believing he failed to find Garou, Saitama returns to his apartment, where he discovers that King, Bang, Bomb and Genos are still there. To his horror, Saitama also comes to the realization that he left his groceries behind at the restaurant in addition to losing his wallet at the store.
Fortunately for Saitama, a miffed Fubuki arrives at his apartment with his cabbage, demanding he apologizes for leaving her with the bill. Shortly afterwards, however, Genos' savior Dr. Kuseno arrives in an armored suit. Kuseno explains that he is concerned for Genos, having received his rescue signal just after he put him back together again.
Dr. Kuseno reveals he has a gift for Saitama; a packet of high-quality beef, which Saitama decides to cook with the cabbage Fubuki just brought with her, in a hotpot. He ends up inadvertently cooking for the entire group. When the food is ready to serve, everyone goes after it at once, splattering the hotpot all over the apartment and fighting each other for the scraps.
Saitama loses his patience and orders everyone to leave soon. Bang looks to Saitama for advice on raising pupils before the bald hero goes to check on King, who got knocked out during the earlier scuffle. The night passes, and everyone except King returns home after the dinner. King wakes up in the morning, and takes Saitama's trash out on his way back. Saitama decides to read a book, although he is disturbed by the loud noises coming from Garou and Overgrown Rover's battle underneath his neighborhood. He checks the TV for any news, but the screen is static. Eventually, tired of the noise, Saitama leaves his house after brushing his teeth and suiting up to investigate the noise. His investigation leads him to a manhole where he heard the noises from, though by now they had stopped.
As he explores, Saitama complains about the constant earthquakes and water leakage, when he suddenly hears running. The naked Gale Wind and Hellfire Flame run into Saitama during their search for Flashy Flash, and decide to take care of him on their way. After Saitama dodges their attacks, the ninjas swear to kill him later, and run off to continue their search.
Saitama eventually runs into Overgrown Rover, who attacks Saitama. Saitama deals a swift blow to the giant canine, knocking it unconscious and sending a massive tremor throughout the entire underground base. He is also attacked by Nyan, who fails to do any damage to him and quickly retreats.
Soon after this, Saitama finds himself at a large gorge, where the Monster King Orochi climbs up from the darkness to face him. Orochi begins to introduce himself, but Saitama cuts him off and tells him his expectations are already low enough and he shouldn't bother. Orochi notices Overgrown Rover is still nearby and is just waking up, so he orders him to kill Saitama. However, when Rover sees Saitama's face, it flees instead, shocking Orochi. The two then share a brief yet incredibly destructive scuffle, but in the end, Saitama comes out victorious. When the defeated Orochi asks him what happened in disbelief, Saitama explains that he just punched him.
Saitama continues walking around as he searches for the leader of the monsters to talk to about the earthquakes and noises under his apartment, defeating every monster that crosses his path. Unfortunately, he doesn't realize that he just killed the Monster King. He bumps into Flashy Flash along the way, who mistakes him for a monster and attacks him. Flash is shocked by Saitama's ability to dodge and defend against his strikes, and finally recognizes him as Genos' B-Class hero sidekick. Flash tells Saitama about the Hero Association's plan and tries to discourage him from going any further, but Saitama deduces that if he follows Flash he might be able to meet more monsters. Flash speeds off to try to shake him. However, Saitama easily keeps up.
Saitama and Flash run in circles searching for monsters. Saitama suggests contacting the other heroes for help, but Flash confidently responds that he doesn't require any assistance, and neither do the other S-Class heroes. Sick and tired of being lost, Saitama punches through the walls until Saitama and Flash discover a monster using a toilet.
Saitama and Flash forces the monster to lead them to the Monster King through a mine cart. The monster estimates that it will take 10 minutes to reach the Monster King. Saitama enjoys the sudden drop down the mine cart tracks, and they arrive in a large cavern where monsters are mining. Saitama and Flash fight off the monsters as they go. At one point Saitama's cape gets caught by a monster, dragging him out of the cart. Flash decides to push on without him, but is surprised when Saitama quickly catches up again with a bag of treasure as well. The two heroes leap across a large gap, still holding their monster guide, and Saitama accidentally drops his bag of treasure into the pit.
As they continue on foot, Saitama, Flash, and the monster are all attacked by Orochi's lurching biomass, which threatens to absorb them. The flesh grasps at Saitama, but can't grip his shiny bald head. Sensitive about it, Saitama angrily punches the flesh away, indirectly causing a distraction that helps Tatsumaki escape from Psykos and Orochi elsewhere.
Tatsumaki uses this distraction to rescue the other Heroes that partook in the invasion with the exception of Zombieman and Flashy Flash, and since Flashy Flash is with Saitama, that meant he was not lifted away with the others as well. Rubble ends up nearly burying him, but he lifts up his leg to stop the debris. He and Flashy Flash are left in darkness together.
Saitama subsequently spends the bulk of the night being ordered to use his brute strength to yank out various pieces of rubble in a very specific order to prevent the makeshift cave from collapsing in on them. The two eventually make it to the surface where they witness the bulk of the upper echelons of the Monster Association fight the heroes.
Although Saitama wishes to join in, Zombieman insists that he stay out of the fight on account of the heroes' pride being on the line. One by one, the monsters fall until only the duo of Black Sperm and the newly born Golden Sperm remains. Afterwards, Garou, freshly turned into a monster, arrives at the scene and effortlessly kills off Golden Sperm and severely wounds Black Sperm.
Garou announces his intentions to kill off a young child that the monsters had taken as hostage and dares the heroes to stop him. One by one the heroes fall before the insanely powerful monster. At this point, Saitama makes his appearance known in a spectacular manner by defeating Evil Natural Water in a single hit. Saitama and Garou do battle, Saitama noting that like he himself usually does, Garou is not even fighting seriously.
As such, in order to 'encourage' Garou, Saitama uses his Serious Table Flip to flip over the largest portion of the Monster Association Headquarters, catapulting Garou so high into the air that he loses track of which way is down, where the two do battle once more, before eventually landing on the makeshift mountain that is the upside down headquarters once again.
As the fight continues, Garou's frustration causes him to continue to monsterize, though as Saitama notes, Garou is actually growing weaker; his later forms sacrificing the skill that was his forte for brute power. Eventually, Garou himself realizes this, as Saitama continues to beat him down before he finally explodes at Saitama in anger.
Garou begins to rant about how the heroes cannot save everyone, and what humanity truly needs is an enemy to unite them against a common threat called 'the Ultimate Monster', and demands to know the reason why Saitama is a hero and the source of his bottomless pit of strength. Saitama's answer of 'it's just for fun' however, only causes Garou to break down emotionally and mentally.
Once Garou finally calms down, Saitama realizes the real reason Garou fights; he wanted to be the hero that would save humanity, but once he realized he could not, he instead decided to 'take the easy way out' and become a monster. In spite of the other heroes' insistence, Saitama refuses to kill Garou on the grounds that he is still human.
Saitama goes as far as to prove this fact by shattering Garou's outer shell and revealing the very much human Garou underneath. Coupled with that, the child that Garou had supposedly tried to kill tearfully rushes onto the scene and reveals that Garou actually saved him from the monsters, twice. Garou is eventually convinced to run away with none of the heroes being able to stop him, or see where he went.
Saitama is formally promoted to A-Class rank 39 and in the process granting him a new, much more luxurious apartment in A-City by the Hero Association. Over the next few days, Saitama collects what remains of his belongings from the rubble of Z-City, where he encounters and ends up unwittingly adopting the now much smaller Black Sperm and Overgrown Rover as pets.
Saitama makes his way back to A-City, where he and his new would-be pets are attacked by A-City's robotic security system. After being questioned by security on how the robots were destroyed, Saitama is escorted back to his apartment by King. There, Saitama plays host to his three 'seniors' in the apartment complex Butterfly DX, Chain'n'toad and Forte.
After his musical fighting style is insulted by Saitama, Forte challenges Saitama to a fight. Saitama agrees on the condition that if he loses, he has to take in the two former monsters that followed Saitama home. Saitama has his easiest victory yet when the Blizzard Group hits Forte with their car in the parking lot during their blind rush.
Entrusting the two formerly dangerous monsters to Butterfly DX and Chain'n'toad, Saitama joins Fubuki as she makes her way into A-City's prison for monsters. Leaving her employees on the ground level, Fubuki explains that they are going to go and see Psykos, the leader of the now disbanded Monster Association. Apparently, when she was in high school with Fubuki, Psykos developed the ability to see the future.
One day however, Psykos saw something so horrible that it made her want to wipe out all of humanity, and now Fubuki wants to know what it is that she saw. Unfortunately, Tatsumaki arrives on the scene, intending to kill Psykos for her earlier defeat and the two sisters end up in a clash of psychic powers over her life while Saitama fights the other monsters who are trying to escape in the ensuing riot.
After dealing with the monsters, Saitama returns to ground level where he stops Tatsumaki from hurting Fubuki any further. The two soon clash, as Saitama takes the fight out into the desert that surrounds the city. Tatsumaki, however, is soon met with immense frustration when her telekinetic powers fail to rip Saitama apart, smash him to pieces or even stop him from calling her a midget.
The pair's fighting takes them all the way to H-City and back; along the way they are mistaken for a Dragon level threat by the Hero Association, nearly crush a family that was moving into A-City, kill a Dragon level monster that was destroying H-City without even realizing it and take down an entire criminal gang without much effort.
Unfortunately for her, Tatsumaki discovers that her already severe injuries from the Monster Association raid have been further aggravated from fighting Saitama and the two of them decide to put the fight on hold for the time being. That said, Tatsumaki thinks she has the last laugh after burying Saitama alive under several hundred feet of earth.
Later on during Tatsumaki's second confrontation with the Blizzard Group, Saitama digs himself out and interrupts another spat between the sisters. There, observing Tatsumaki's severe injuries, he points out to the Blizzard Group that this is their one and only chance to make Tatsumaki leave them alone for good, to which they declare their intentions to get strong enough so that not even a Tatsumaki in full health can stop them.
As soon as Tatsumaki vacates the scene, Saitama shortly follows suit, intercepting her to speak with her. Predictably, she rebukes his approach, denouncing him for hiding his true strength, although Saitama speaks to the contrary, giving an eyeroll response to her boast that she could take care of him in five seconds if in perfect health.
Saitama asks Tatsumaki why she is in the Hero Association if she hates human contact so much. Tatsumaki goes on to state her reasons, only to retract them soon after flying off again, leaving him to wonder what the term "Bla-" means.
Saitama later arrives at the Hero Association HQ, where he sees Forte, Butterfly DX, and Chain'n'toad. Saitama tells the three heroes not to come into his house without permission. Surprisingly, Forte apologizes to Saitama for his rude behavior earlier. Seeing Saitama's current state, Forte offers his clothes and shoes, which grosses Saitama out. It is revealed that Forte saw Saitama from the hospital room, fighting. He tells Butterfly DX and Chain'n'toad that they are no match for Saitama. The three heroes then decide to be accepted by Saitama.
After Genos defeats the Forest King, Genos challenges Saitama to a duel, which Saitama accepts. When they fight, however, all that Genos manages to do is temporarily blind Saitama before he stops, claiming that the best he could do is get Saitama dirty. Saitama admits that he cannot tell if Genos has gotten stronger, only a lot brighter, which only further depresses Genos. Genos comes to the realization that Saitama was not even remotely threatened by his attack just now. Genos explains to Saitama that when he first agreed to take him on as a pupil, Saitama told him to try and climb to the top of the Hero Association, but that has gotten him nowhere. Genos also explains that the Hero Association is dying.
At this point, the public's opinion of the Hero Association is that it takes their money to pay increasingly incompetent people, who barely hold back the monster threat and usually cause as much, if not more, property damage than the monsters they fight. Another group, calling themselves the Neo Heroes has been created in response to this public outrage.
The Neo Heroes claim to have taken a look at the mistakes made by the Hero Association and seek to correct and improve upon the formula, claiming to have two thousand possible candidates selected, including pro heroes from the Hero Association itself. Genos' question is, if Saitama thinks that they should transfer over to the Neo Heroes, as he feels with a higher standard set, he might become stronger.
The subject changes over to why Genos is so obsessed with becoming stronger. Saitama voices a thought that had been bothering him for a while; that he could have simply killed the cyborg Genos had been hunting for the past five years. Genos admits that it is a possibility, but he is still preparing for the day that the bout finally comes, before changing the subject back and asking Saitama if he wishes to transfer over to the Neo Heroes, to which Saitama says no. Upon hearing this, Genos says he won't either.
Arriving back at HQ, the pair discover Forte as he finishes constructing a dog house for Black Sperm and Rover. Saitama introduces Forte as his neighbor and seeing as how Saitama does not wish to move out of his cramped little apartment and he cannot move in with him, Genos takes Forte's apartment.
Saitama plays video games with King and keeps losing, much to his annoyance. King becomes depressed after winning the game, as it reminds him that he is a fraud. Saitama tells him to work on his muscles. Flashy Flash appears at the apartment and introduces himself to Saitama, but Saitama closes the door in his face. Flash states he has business with Saitama and threatens to kick the door in. Genos sees Flash and engages in a squabble with the hero outside the apartment.
An exasperated Saitama opens the door to demand that they stop fighting in front of his new house. Flash reminds Saitama that he had broken his sword, and Saitama offers to fix it with duct tape. Flash refuses the offer and presses Saitama to remember his name, only to become annoyed when Saitama cannot remember. Flash changes his mind about the sword and demands reparation, so Saitama tells Genos to grab duct tape, and Genos runs off. Flash joins Saitama in his apartment and tells Saitama to become his disciple. Without waiting for a response, the ninja leads Saitama out the door, but Saitama closes the door shut when Flash steps out. Becoming increasingly annoyed, Flash demands that the Caped Baldy stop messing around and follow him to train, only for Saitama to state he can never get along with someone if they refer to him by his hero name. Challenging Saitama to a fight using his real name, the two heroes then journey to a training site in the Hero Association headquarters.
Flashy Flash states the time limit for the match would be thirty minutes and that he would not be using any weapons, with the stakes being that if Saitama landed a single hit on him, the bald hero would win. Otherwise, he would have to follow the ninja as a disciple. Announcing the start of the match, Saitama instantly catches Flash off-guard, directly moving in front of him to attack, with the ninja just barely managing to dodge. Recovering from the move, Flash declares the same move would not work on him twice, to which Saitama once again appears directly in front of him for another attack, which the ninja barely dodges. After nonchalantly enduring some of the ninja's attacks, Saitama questions if Flash could keep up the effort for thirty minutes as he is already sweating and wobbling. Internally correcting the bald hero that these are merely symptoms of anticipation and excitement at fighting a challenging opponent, Flash briefly gets lost in the moment and attacks Saitama with his Flashy Fist. After worrying he had gone too far, Flash is amazed to see that the bald hero is completely fine. The ninja then declares that he will use weapons after all in order to simulate a real battle, with Saitama internally wishing he had brought a fly-swatter.
Becoming increasingly unnerved with how easily Saitama is keeping up with him, Flash tries to use his sword to attack, only for it to break when the bald hero catches it with his teeth. After the ninja accidentally backs himself into a corner, Saitama moves in for a Death Punch. However, the fight is interrupted when Genos returns and informs the heroes of a Demon level monster alert that has shown up in City-E.
Saitama immediately turns his attention to the alert, turning away from a disturbed Flash. Rebuking the request for a rematch, Saitama refers to the match as a simple game of hide and seek. Declaring that they have to deal with the monsters first, Saitama states they will fight again later on, just as long as the ninja does not get in the way of his hero activities, then turns to leave after once again failing to remember Flash's name, horrifying the ninja.
Saitama, Genos and Flash then arrive at City-E, where the Internet Surfers are causing chaos. While there, they also encounter Speed-o'-Sound Sonic, who was waiting near the monsters in order to face Saitama again. Flash and Sonic notice each other, with the latter becoming indignant at the fact the former is accompanying the duo and asks Saitama why he is with the other ninja. Saitama and Genos briefly discuss whether or not the Demon alert was attributed to Sonic and not the monsters, before a fight breaks out. While Flash and Genos easily dispatch the monsters, Sonic heads straight for Saitama who promptly knocks him out once again.
Later on, Saitama is back in his apartment with Genos and Flash, discussing Sonic's latest appearance. Saitama guesses that it is the fourth time that the ninja has tried to sneak up on him, while Flash is amazed that Sonic went straight for the bald hero instead of himself, noting how their fates are connected. Saitama asks whether or not the two ninjas are friends, which Flash quickly denies, beginning to explain how they knew each other before going silent, horrified that Saitama remembers Sonic's name and the subsequent implication that the ninja is more dangerous than he thought. Flash then tells the duo that his history with the other ninja is long, but feels like he needs to explain it. Saitama quickly tells him that if it is too long to just forget about it, though the ninja continues regardless.
Flash explains his and Sonic's harsh upbringing in the Ninja Village facility and how the other ninjas helped him recover the human emotions that were being stripped away by the harsh training and frequently helped him without asking for anything in return. After hearing Flash talk about how he spared Sonic's life on the day he massacred the Village by making him eat a poisoned stew, Saitama notes that there are still some stew ingredients left over in his fridge.
Saitama later decides to pay Sonic a visit, having discovered one of the many challenge letters that the ninja sent to him which contained his address. Genos questions his master as to why he wants to pay the ninja a visit. Saitama replies that he is annoyed that Flash keeps pestering him about his broken sword, so he wants to see Sonic for a replacement that he can give to the other ninja. When the cyborg points out that Sonic is not the type of person to part with his sword easily, Saitama states that he will simply snatch the sword after sending the ninja flying. The bald hero also says he wants to sever the connection between their fates, although he notes there was never that much of a connection to begin with.
While waiting for Sonic to arrive back at his hideout, Saitama encounters the Ninja Village Leader, swiftly takes him out and confiscates all of his weapons and equipment. When Flash and Sonic arrive, Saitama gives all of it to them, hoping to finally pay back Flash for his broken sword.
Saitama later meets Genos after a grocery run. Genos requests another sparring bout with Saitama, explaining that he wants to collect data on his physical abilities for Dr. Kuseno. Saitama agrees. Suddenly, Sweet Mask approaches them and invites Saitama for tea and a chat.
The next day, Saitama and Sweet Mask go to a cafe. A waiter takes their order. Saitama says he wants a coke, but Sweet Mask ignores him and orders him a shiso ginger ale instead. This irritates Saitama, and he sits through Sweet Mask's entire lecture without hearing a word.
Later, Sweet Mask treats Saitama to a meal, which he calls "high-intensity training." He tells Saitama his plan to make him a better hero and introduces the staff members who will assist him, but Saitama shows no interest in anything he proposes and tells him that he performs hero activities for fun. Sweet Mask takes Saitama on a stroll in a park, where he reveals his plan to make Saitama the ideal hero. Saitama's bored expression frustrates Sweet Mask, so he makes a snap decision to cheer him up at a nearby amusement park.
On a Ferris wheel, Saitama listens as Sweet Mask explains his backstory and his ideal hero project. Saitama refuses Sweet Masks's proposals, feeling that the flawless hero Sweet Mask idealizes is not the free, unconcerned hero he wants to be. He excuses himself from the conversation and jumps out of the Ferris wheel to head to his planned sparring bout with Genos, leaving Sweet Mask behind.
On the way to the bout, Saitama runs into Genos heading in the opposite direction. Genos postpones the spar and explains the dispatch orders to assist Sweet Mask in fighting Pesky Clown. Saitama joins him. On the way to the fight, a broadcast reporting Sweet Mask's monster identity catches their attention. Saitama tells Genos he is going ahead and jumps to the amusement park. He arrives at the scene to catch a stone a bystander casts at Sweet Mask. Sweet Mask asks Saitama to kill him in order to take advantage of the crowd's attention and gain recognition, seeing that his time as a hero is over. Instead of going along with the request, Saitama sympathizes with Sweet Mask's predicament, and he flees the scene with Sweet Mask in tow.
The next day, Saitama brings Rover's caretakers cheap dog food. The Hero Name Victims Association, a group of heroes discontent with their given hero names, approaches him and asks him to be an executive for their faction.