The origins of the person who is known as Number 6 are unknown. Apparently he was "created" and raised by the Villain Factory, and since his creation he spent time watching anything related to the hero O'Clock, for which he had great admiration. At some point in the past, he watched as O'Clock's career fell apart and his face was seriously injured, leaving a scar that runs diagonally across his face.
As a sign of respect for him, he self-inflicted on his face a scar similar to O'Clock's wound, becoming known as Number 6. He eventually acquired Overclock, the Quirk of his beloved hero, from All For One, the man who stole it in the first place.
The first time Number 6 is seen in action is during Kuin Hachisuka's defeat. After Knuckleduster defeated her and removed the Queen Bee that controlled the body of his daughter Tamao, he killed the Queen Bee and destroyed the entire swarm with an explosive device. However, one of the bees managed to survive and escape.
Shortly after, Number 6, disguised as a cop, walks down the street as he sings to himself about data and bees, while tossing a small plastic capsule in the air. He notices the last of Kuin's bees shakily flying through the air past him. In a flash, Number 6 jumps up and catches the bee in the plastic capsule, before leaving the place.
Days later, Number 6 acts again to wreak havoc. For this occasion, disguised as a member of the staff, sneaks into the shooting set where Ingenium and Captain Celebrity were shooting an ad. Using a device, he causes a truck to crash, releasing a NLV known as Bat Villain, which was defeated and arrested weeks ago by Ingenium and the Naruhata Vigilantes. Bat Villain wants to take revenge for that, but is easily defeated by Captain Celebrity.
After this, Number 6 is in charge of illegal importation of Trigger to Japan, for its subsequent distribution, through the so-called "Crab Route". The Police Force, lead by Naomasa, carries out an operation to dismantle the distribution of the drug and arrest those responsible. The clues lead them to the SS Mall in Super Minami in the city of Osaka. There, the drug is distributed through the country hidden in Kanidoge's food packaged. For this operation, they have an infiltrated agent, Monika Kaniyashiki, as a worker in the Kanidoge chain; and Fat Gum in case of needing a Hero for the operation.
Monika goes to the SS Mall loading dock and she discovers that Trigger was indeed hidden in the packaged. She also discovers the criminal responsible for that, disguised as a part-time worker. Having been discovered, Number 6 congratulates Monika and uses his Quirk to snatch her gun and a tablet with vital information. Monika quickly takes cover and requests for reinforcements, so Naomasa, Fat Gum and the rest of the police forces come to the place to catch the suspect.
Despite being surrounded, Number 6 is calm and confident, and before anyone can stop it, he introduces a code on the tablet that causes the Kanidoge's Mechs employed by the workers are out of control and go on a rampage. Thanks to Fat Gum and Monika, the workers are rescued and the mechs are neutralized. While the villain congratulates them for their actions, detective Naomasa gives him a warning shot, assuring him that next time he won’t miss.
Monika warns Naomasa to be careful, as the villain has an acceleration quirk that gives him extreme speed. Taking into account this information, Naomasa orders the speedster villain to get on the ground slowly. The villain just smiles. Without noticing, the damaged mechs approach the batch containing Trigger and explode, destroying all evidence. The villain takes advantage of the distraction to flee with the remaining pieces of evidence using his quirk.
The police chase Number 6. As he‘s not giving up even after verbal commands and warning shots, Naomasa orders to open fire against him. Number 6 uses his speed Quirk and dodges all the shots, but the detective shoots once more, injuring him in the leg, after deducing that the villain’s Acceleration Quirk needs a few seconds of cool down time after using it. The police rush on to the injured criminal.
Confronted by the police, the Villain uses his quirk and the time seems to freeze. He gets away from the cops. His wound does not seem very serious since he was just got grazed by Naomasa's shot. The speedster villain checks that they use rubber bullets, and in a blink of an eye, he disarms a whole group of cops and shoots into their bulletproof vests with their own weapons. Although this does not kill them, it does leave all the policemen very badly wounded. The villain being able to finally escape with the remaining pieces of evidence without any problem.
Several days later, in an unknown apartment, Number 6 is training his Acceleration Quirk hard, to bring it to its limits. From an earpiece, the Villain Factory Employer tells him that his training is unnecessary, that he only needs to use firearms as he did in Osaka, but Number 6 replies that he is more partial to punching power. The voice tells him to do what he wants, that at least they get data about his physical state while accelerated. The call ends, and the speedster villain talks to himself that he only uses firearms when he is gets backed into a corner because guns are unheroic, as he contemplates a large O'Clock poster.
After this, Number 6 continues to carry out the works commissioned by the Villain Factory, such as releasing the Next-Level Villains through the streets of Naruhata to collect data and obtain samples, as he did with Octoid. After a tough fight against Koichi, Aizawa, the Hotta Brother and Kamachi, Octoid is forced to escape, fleeing into an alley, being pursued by the others. However, Number 6 finds him first and defeats him easily, obtaining a sample of his body. When he was about to leave, Octoid throw a stone at the speedster villain, causing him a slight scratch on his face, but that greatly angers Number 6, which almost kills Octoid from a beating before he is forced to leave due Koichi and the others aproaching.
Number 6 is also in charge of looking for people with powerful Quirks for the Villain Factory. To do this, he distributes a new variant of Trigger that is administered orally. It is less effective than the old form but lacks the psychotropic element. As this new drug does not turn people into full-blown villains, it makes it easier to distribute on the street, and therefore, it benefits the Villain Factory, because it makes easier for them to showcase potential candidates to kidnap and transform into Next-Level Villains. The police manage to catch and interrogate one of the distributors, and the investigation led the police to the place where the deals were happening, but Number 6 had already cleared out.
Recently, Number 6 has set himself the goal of kill Captain Celebrity. To achieve this, he decides to take a test attack with a special Next-Level Villain: the Bomber. After the Captain celebrated Christmas at Marukane's department store with the Marukane Performers, Number 6 sends the bomber to hijack the taxi where the Little Sisters of Saint Lila’s Academy are. Captain Celebrity goes out in pursuit, but just when he is going to reach them, Number 6 causes the creature to explode with a device.
Using the aerodynamic barrier of his Quirk, Captain Celebrity manages to protect the girls, leaving unharmed of the explosion, although when doing it he lowers his own protection, suffering several wounds, although nothing really serious. The witnesses come to Captain Celebrity to congratulate him for what he had just done. Meanwhile,Number 6 observes everything on top of a building. With his attack, he manages to deduce the weak point of Captain Celebrity’s Quirk and decides to leave the place to prepare a new attack to end his life, releasing more flying bombers.
After the incident, Captain Celebrity announces that he will return to the United States of America. And for this, his friends decide to organize a big farewell party at the Tokyo Sky Egg in several weeks, where some of the most famous heroes of Japan will participate and that thousands of people will attend. And it will be at that moment when Number 6 carries out his plan to assassinate Captain Celebrity.
However, Naomasa and the police are still on his trail; and thanks to an arduous investigation and a series of informants who give them important data, they manage to find what turns out to be the laboratory where the Villain Factory transforms the people who they kidnap into Next-Level Villains. The same day on which the Celebrity Farewell Party is celebrated, the Police Force, along with the heroes Eraser Head and Fat Gum, prepare to raid Onomura Pharmaceuticals Kanto R&D Center.
When Naomasa gives the order, the police and heroes raid the place, arresting as many suspicious persons and seizing all possible evidence of illegal experiments. They hardly have any problems at first, thanks to Eraser Head and Fat Gum, who defeat the main threats, but when they arrive at the secret laboratory, they meet one of the Bombers. When the creature prepared to self-destruct, Eraser Head cancels his Quirk with his Erasure, and Fat Gum launches on him to neutralize it. However, they discover to their horror that behind the first Bomber there are several more, too many for Aizawa to cancel the Quirks of all of them. And behind the creatures, is Number 6, who presses a device generating a huge explosion in the laboratory.
Number 6 manages to escape the explosion by grabbing the leg of one of the five surviving Bombers. The Villain admits to himself that, although he expected the authorities to end up discovering the place, he was not expected to do it so soon. Despite this setback, he decides to continue with his plan to kill Captain Celebrity, heading with the Bombers to the Tokyo Sky Egg.
Upon reaching the area near the Sky Egg, Number 6 starts up his plan: one of the bombers sticks to the glass and explodes. This makes Koichi, who was near the place of the explosion, almost falls to the ground, while Captain Celebrity, after making sure that Koichi is well, goes out to face the creatures.
One of the Bombers explodes, hardly affecting him, but everything turns out to be a distraction, as an especially large Bomber clings to the tower of the Tokyo Sky Egg and explodes, seriously damaging the infrastructure, threatening to collapse with thousands of innocent people inside. To prevent the tower from falling, Captain Celebrity uses his enormous strength to hold the building, but this leaves him helpless.
Everything is coming out just as Number 6 had planned, and sends one of the two remaining Bombers to attack him. It is a creature that was specially designed to face Captain Celebrity, with six arms, the ability to throw explosive punches and to regenerate any lost limb. The creature mercilessly attacks Captain Celebrity, but despite the punishment he received, he continues to hold the building, ensuring that he can withstand hundreds of those more attacks.
In the Tokyo Sky Egg dome, both the heroes and the audience are wondering about the many tremors rocking the dome. Some try to use their communication devices to contact the outside or other departments to know what is happening, but the remaining Bombers generates an EMP blast, causing a blackout in the building and cutting the cell signals. In the distance, Number 6 is satisfied with the result, because it prevents anyone from helping Captain Celebrity. With this situation, Best Jeanist takes the lead and deduces with more or less the intentions of the person responsible for what happened, so he devised a plan so those heroes capable of flight will exit and make contact with the outside.
Meanwhile, Captain Celebrity continues to hold the damaged structure so that it does not fall, while resisting the Bomber's attacks. When the creature prepares to attack him again, Koichi Haimawari appears and uses his Quirk to shoot the repulsion force blasts at the Bomber and blowing up his fists. Koichi's plan is to endure as long as possible protecting Captain Celebrity until someone can help them.  The plan works. Koichi manages to stay long enough until the first heroes begin to arrive to assist them in their battle against the Bombers.
In the distance, Number 6 sees the Pro Heroes managing defeats his creatures while securing the building. He gets very angry when he sees how his plans are being dismantled by the heroes and decides to carry out his last move to kill the greatest number of people, in revenge for their interference. The Bomber that was attacking Captain Celebrity clings to the supporting tower. Number 6 uses his device to cause the creature to self-destruct in an explosion so powerful that the Tokyo Sky Egg begins to fall down.
The number 6 contemplates the collapse of the Tokyo Sky Egg, ensuring that only a god can save them now. However, Detective Naomasa managed to call All Might on time and, with an inhuman feat, it takes him only a few seconds to reach the place and, in a flash, he lands the Tokyo Sky Egg dome safely. After witnessing that feat, Number 6 feels increasingly furious to see how his act of revenge had been totally ruined by All Might’s intervention. However, he does not give up, and uses a device again to reactivate the Bombers remains.
The remains start to regenerate, combine and grow into a gigantic and uniform mass of flesh, that bursts releasing a swarm of two hundred mini Bombers to attack everyone. Number 6 is confident that even All Might will not be able to destroy all the creatures, so he is sure that this attack will cause some deaths. He is wrong once again. All Might destroy the entire swarm with his Nebraska Smash, saving thousands of lives again.
Number 6 cannot believe that his plan has failed again because the impressive demonstration of power of All Might, but unlike the previous time, this time he can not help but laughs, unable to conceive of how a being as powerful as All Might can come into existence. Suddenly a voice from his earpiece speaks to him, assures him that what he have seen is real, and the main objective of the organization is to create something at the same level as All Might. With all the Bombers wiped out and the laboratory destroyed, Number 6 decides that the only thing he can do is disappear for a while.
Without knowing it, he is being observed by Knuckleduster through the scope of a sniper rifle. The vigilante had deduced that the Villain Factory would attack the Tokyo Sky Egg and looked for the best place to snipe their agent. Unfortunately, when he is about to shoot him, a bird passes in front of his scope, causing him to miss the shot and piercing Number 6 shoulder. Knuckleduster tries to shoot him again, but the villain quickly locates him, and despite his injure, he jumps from building to building thanks to his Quirk until he ends up on the rooftop where Knuckleduster is.
Number 6 recognizes Knuckleduster as the former hero O'Clock, whom he admires so much. For his part Knuckleduster recognizes him as the villain who is behind all the Next-Level Villains attacks and is also in possession of his former Quirk Overclock, but otherwise, he has no idea who he really is. The villain replies that he is a nobody, a thing still unformed, and he has no real name, he is just called Number 6. However, he confesses to Knuckleduster that he hopes to become O'Clock, since he admires him a lot, and he asks him to recognize him as his successor.
Knuckleduster refuses to grant his request, in fact he does not intend to allow a villain like him, who is in possession of his stolen Quirk, to continue to exist. Number 6 resigns to the fact that his idol recognizes him as a villain, and attacks him. But Knuckleduster knows all the weaknesses and drawbacks of his former Quirk, and uses them against Number 6, causing him to fall into a trap.
Knuckleduster blows up the rooftop and several floors below. Unable to maneuver in the air, Number 6 falls to the bottom, being shot several times by Knuckleduster with a shotgun while falling. Once on the bottom, the vigilante continues to beat him. Knuckleduster admits that killing him was his best long-term option, but now that he had fallen into his trap, it is worth capture him to interrogate him. Knuckleduster tells Number 6 that the building is damaged, and therefore another blast will gonna bring the whole building down, becoming his tomb. He can’t escape even with his super speed.
Number 6 tells him he is naive, because his decision to no kill him gives him the chance to strike back. Number 6 confesses to Knuckleduster that he has bomber cells in his body, as parasites, before self-detonating his left arm, blowing Knuckleduster away. Seriously injured, Number 6 praises Knuckleduster for his stubbornness, considering him as the best hero, even better than All Might himself. However, he is going to surpass him, and be the new O'Clock. Knuckleduster tells him that that will not happen, because in addition to his injuries, he will end him.
Number 6 shows Knuckleduster that, although he doesn't know as much about Overclock as he does, he can do things with the Quirk Knuckleduster could never achieve. Combining overclock with the Bomber's cells of his body, he accelerates the growth of the cells, obtaining an explosive arm where before his left arm was, then, he extends the cells to the right arm, thus obtaining two explosive arms.
Despite all this, Knuckleduster is willing to face him and attacks without contemplation. Admiring Knuckleduster's resolve, Number 6 recognizes that he is certainly the best, before attack him, initiating the final battle between both.
Days later, the police investigate the scene of the confrontation. The only thing they find there are blood samples that correspond to Knuckleduster and Number 6. According to the police lab, Number 6 blood type and DNA is mixed with a number of other chemicals. Tanuma, who lead Trigger investigator and knows the truth about Knuckleduster, questions if "the thing they're chasing" is even human.
While acting as the manager, one day he reports to girls members that, as Narufest was becoming less and less popular, the Marukane's executive have decided that next month's Narufest will be the last, which shock the girls. The manager apologizes for not having managed to convince them of the contrary, but Miu comments that decision was predictable, although Kazuho is sad.One day, posing as Rokudo, he finds Kazuho singing in the street, helping her against three thugs that were making fun of her, until the police arrives and they quickly leave the place. Then both go to a cafe to talk about her solo project. Kazuho explains that she tries to craft a future for herself beyond the Narufest, now that it's about to end. "Rokudo" wants to help her on her project, and asks her to let him listen to her song, and gets so move about the lyrics that he starts crying, and tells Kazuho that her song is amazing.
On the way back, Kazuho and "Rokudo" meet again with the trio thugs who had made fun of Kazuho earlier. The leader is angry because he considers them responsible for the police hassled him, and attacks them. To everyone's surprise, Nomura retains him with a hold and advises the thugs to quit picking fights as he is a hero, showing his hero license to prove it.After a meeting at the Marukame, "Rokudo" agrees with the attendees who will contact the FeatherHats members for the last performance. As soon as the meeting is over, Kazuho and Nomura leave quickly to carry out a street performance. After changing her clothes, he tells her that she has the permits so she can sing without problems. Kazuho sings one of the songs she had composed and to which Nomura had given a few tweaks, and the performance has a great success among the attendees.
After this, Kazuho and Nomura celebrate their success at a bar. There, they meet the three thugs of the previous day but instead of causing them problems, they congratulate them. fter finishing drinking, Kazuho and "Rokudo" walk back through the streets. At that moment he confesses to Kazuho and tells him that he wants to do everything possible for her. Even though Kazuho is flattered by his words, his feelings are unrequited, and her songs are to give herself courage. She leaves giving thanks to Nomura for everything.
At that moment the three thugs appear, which are actually his friends, to cheer him up. It turns out that "Rokuda" had developed feelings for Kazuho, and he crafted his personaand organized that whole act specifically to get Kazuho to like him. His friends tell him to be himself after Kazuho rejects him. Number 6 decides that they're right and he no longer needs them. He gets rid of his Rokudo Nomura facade and attacks them.Later, he receives a call from Kazuho, who is crying heartbroken. She apologizes for rushing off earlier and tells that she needs him to be there for her. Sitting on the beaten bodies of the thugs, Number 6 replies not to worry, that he will help her, since he is her fan and will always be on her side.
Next day, while posing as Rokuro Nomura, Number 6 meets with Kazuho in a cafe. Kazuho explains that she wanted to talk to someone she is close to (Koichi), but in the end she couldn't do it for an unknown reason. Number 6 suggests that maybe is because she didn’t get the timing right, to which Kazuho agrees.
Internally, Number 6 is glad he got it right with his response. He is imagining his “master” O’Clock giving him advices on how to use his Quirk Overclock to interpret person's subconscious reactions to both manipulate and react to their reactions without the subject even knowing. With this ability he can give her the correct answers and the words that Kazuho wants to hear.Back to the conversation, Kazuho says that she still has no confidence in herself. She says her family and friends only know a part of her and she is afraid of being rejected if they know how she really is. Number 6 tells her that will not happen because everyone loves her, and after suggesting a change of scenery, he tells her that what she needs is to calm down, take stock and examine her feelings and then have healthy communication with all of them. Kazuho agrees and leaves the cafe with him. While walking down the street, Kazuho is glad to have "Rokuro" with her, since he is a kind and honest person, although "Rokuro" denies him saying that he actually has a passionate side and a complex inner life. Kazuho takes his words as another of his jokes, and Rokuro decides to invite her to his secreat hideout, in the basement of a ruinous looking building. Kazuho accepts their invitation, and once they are there, Number 6 decides to stop his facade as Rokuro Nomura and reveal his true self.
Before Kazuho can react, he pushes her into the room and locks her up. That basement is where Number 6 had hidden and took care the only surviving bee that he rescued from the fight between Knuckleduster and Kuin Hachisuka two years ago. During all that time, he had been feeding it with victims, until the bee regained strength and became a new Queen Bee, forming a new swarm. Now all that was needed was a new host which the queen bee could parasitize, and number 6 had decided it was Kazuho.
Because Kazuho is missing for several days, her family informs the police of her disappearance and her friends and acquaintances go in search of her, walking the streets of Naruhata, unaware that Kazuho had been parasitized, becoming Queen Pop. Koichi is one of those who are looking for her, so Number 6 decides to announce the arrival of the "new Kazuho" with a spectacular show as well as destructive.
Queen Pop attacks Koichi with several Boom Bees, generating several explosions that attract large numbers of people to the place. Seeing people begin to gather, Number 6 tells Queen Pop that it is time for her performance to begin.
To the rhythm of a song that they composed, Queen Pop uses her Quenn Bee Quirk to release several Bomb Bee that explode at random, rampaging the streets of Naruhata. Number 6 witnesses how Koichi tries to stop Kazuho, failing in his attempt and being shot down and rejected by her, proclaiming it's over for Koichi, as Kazuho is not his little princess anymore but a queen.