Taishiro Toyomitsu/Synopsis

History
Fat Gum worked with the police, becoming familiar with cases involving Quirk enhancing drugs and arresting its users.

Vigilante - My Hero Academia: Illegals
He chases down a criminal and slaps him for making him drop his takoyaki.

When an exploding cargo robot threatens participants of the Mascot Idol Carnival, Fat Gum absorbs the explosion with his Quirk.

Internship Arc
Walking through Eshuha Market, Fat Gum eats an entire board of takoyaki while on patrol with Tamaki Amajiki and Eijiro Kirishima. Suddenly, a group of criminals appears, and Fat Gum stops them from running. When one of them escapes Tamaki stops him from fleeing. Fat Gum then praises Tamaki, until he notices the appearance of a shooter and tells everyone to get down. Fat Gum then charges towards him.

Fat Gum tells his interns not to rush and instructs Tamaki to leave the area with him. When Tamaki reveals his Quirk will not activate, Fat Gum stops and questions the shooter if they have a Quirk eraser.

Intercepting a villain following his fight with Eijiro, Fat Gum teaches him to capture without any victims, discussing the villain's drug afterward. Fat Gum then states that it was an inferior version of the drug he had encountered before. After examining the pieces of a broken bullet, he is surprised to learn of the effects of the drug which was making Quirks unusable. A few days later, Fat Gum attends the meeting regarding Shie Hassaikai in Sir Nighteye's offices.

Inside Sir's offices, Eijiro approaches Fat Gum asking about Shie Hassaikai. Fat Gum mentions he has quite the connection with them. During the meeting Ken Takagi remarks that they cannot talk with students around, Fat Gum calls Eijiro and Tamaki as important witnesses and proceeds to introduce them himself. When Sir mentions unlicensed goods have become part of Shie Hassaikai, he requested help from heroes familiar with that line of work. Fat Gum mentions that in battle Tamaki was shot by a drug that erases Quirks, and due to Eijiro deflecting the bullet, they were able to examine it, finding out that it contained human blood and human cells. Asked how it connects to Shie Hassaikai, Fat Gum reveals that there has been contact between them and an organization selling it.

When Sir reveals he would like everyone to assist in searching multiple locations. Fat Gum accuses Sir of thoroughly tiptoeing about while Eri is probably crying. Sir says that they will not become like All Might and that they should bring their chances of saving her as close to 100% as possible. Shortly afterward, Sir thanks everyone for their cooperation and the meeting ends.

Days later, when everyone is gathered together, Sir reveals that Eri is at the base and that they received new information from a member who was purchasing a toy a few days ago. Sometime later, the group of Heroes and Police Force gather outside the base of Shie Hassaikai. When the police finish reading the warrant, Fat Gum is surprised when Rikiya Katsukame crashes through the door and knocks the police officers into the air. Ryuko Tatsuma's group takes on Rikiya while the others head forward. Fat Gum tells everyone to get inside. Once inside Fat Gum apologizes for tracking in dirt and tells those behind him to forget about watching out for suspicious behavior. Upon reaching underground, the group believes it to be a dead end. Mirio Togata discovers a wall blocking the way, which Fat Gum calls a 'cheap trick'.

After Izuku and Kirishima knock down the wall, the floor starts to warp due to Joi Irinaka's Mimicry Quirk. Fat Gum asks Shota if he can erase Joi's Quirk, but the floor suddenly opens up, dropping the Heroes and interns into a room with three of the Eight Expendables. Fat Gum prepares to fight until Tamaki stops him. When Toya Setsuno and Yu Hojo draw their weapons, Fat Gum tells them that their blade and bullets will sink right into his body. Tamaki restrains and disarms the three yakuza and tells the others that he can handle them. Fat Gum instructs everyone to get moving because Tamaki surpasses them all in terms of ability.

Making their way through a corridor, Fat Gum overhears Izuku and Eijiro discussing Tamaki. He tells the two that the mark of a true man is to have the ability to completely trust someone who has their back. Suddenly, Shota gets attacked but Fat Gum shoves him out of the way and is shoved into another room. Getting up, he is surprised to see that Eijiro is in the room with him. Eijiro tells Fat Gum that he was also trying to protect Shota but once he did, he was swallowed by the enemy's Quirk. As they get up, Fat Gum states that they should brace themselves. All of a sudden a member of the Eight Expendables Kendo Rappa appears, launching rapid punches at great speed, striking them both. Fat Gum counters with a punch of his own, but is surprised that his punch strikes a barrier instead. Fat Gum encourages Eijiro to be unbreakable because if his spirit breaks, then they are done for, and that eliminating villains is about making them lose the will to fight. He asks Eijiro what they will do if their spirits are broken before theirs.

Once again they were attacked by rapid punches but Fat Gum withstands the attacks and taunts Rappa into a fight to determine who is stronger, Rappa's punches his own body, demanding that they duke it out. Fat Gum absorbs the punches and takes in a lot of energy, which burns away his fat and making his defense weaker. Eijiro appears in front of Rappa and is defeated shortly. With his fat body disintegrated, Fat Gum thanks Eijiro for his work.

Dashing forward, he picks up Eijiro and then tells the yakuza that they are going to lose all because they underestimated Eijiro. With his spare hand, he unleashes a powerful blast knocking out Rappa.

Fat Gum asks Eijiro if he was conscious, and Eijiro looks at him confusingly as Fat Gum claims he must protect him. Fat Gum thinks back to their first meeting. Suddenly Rappa stands up claiming it to a battle to the death. Fat Gum questions about it being a trap, but Rappa denies it. Rappa explains he wants a fight where they kill each other. Praising them, he vows his interest in them both. Walking away he says that at their next match he will not be as merciful. Fat Gum explains that he is going to be arrested and locked up and that there will be no next time. Rappa refuses to listen and replies that if no one is dead, then it is a draw. Fat Gum moves Eijiro to an infirmary and asks Rappa what he was doing working for a gang. After hearing his explanation about Kai Chisaki, Fat Gum begins to become concerned and proceeds to ask Rappa about Chisaki's plans.

Pro Hero Arc
Fat Gum, along with Ken, is seen commenting on Hawks' arrogance during the JP Hero Billboard Chart.