The Fat Gum Agency, is a large building with a rounded roof located between two others. The main facade of the building is decorated to mimics the appearance of Fat Gum himself. The upper part looks like the BMI Hero's face, with a black area representing his mask with two round windows simulating his eyes. Below this area there is a row of windows positioned so that reminds Fat Gum's distinctive smile.
The bottom of the facade has the initials of Fat Gum alias, with an F and an inverted F on the sides and a G surrounding the entrance door. The words "Fat Gum" are posted just between the initials as well. On the left side of the building there is a decorative element that represents Fat Gum's arm holding a takoyaki ball.
Inside, the office is austere, with a table, a huge dark chair and a few furniture.
The first time was to stop the illegal introduction of drugs into the country, taking advantage of a Mascot Idol festival at the SS Mall in Super Minami, Osaka. The villain responsible for that operation was discovered, but he activated a code that drives the mechs to start rampage the place.. Although Fat Gum manages to avoid any casualties, in the attack the mechs destroy all the evidences, and the villain manages to escape after hurting numerous policemen.
Weeks later, the police discovered the Villains Factory's base of operations, the Onomura Pharma Corp. Naomasa contacts Fat Gum to work with Eraser Head and Monika, first to investigate people connected to the company,  and later to participate in the police raid on the pharmaceutical company. There they meet again with Number 6, surrounded by creatures known as Bombers. Number 6 blows up the labs, fleeing with the Bombers to the Tokyo Sky Egg.
At some point, Fat Gum accepted Tamaki Amajiki to work at his agency. Although Tamaki proves to have great potential as a hero, his lack of spirit prevents him from standing out. Fat Gum tries to help him in this aspect. After a long time, following Mirio Togata's advice and with the help from Tamaki, Eijiro Kirishima ends up interning under Fat Gum as well.
While patrolling the streets in Esuha Market, the three face a group of villains, and although they manage to defeat them, Tamaki is hit by a special bullet that temporarily nullified his Quirk. Fat Gum is worried, because it is the first time he knows the existence of a drug that cancels the quirk.
A few days later, Fat Gum, Eijiro and Tamaki attend a Hero Team Up meeting in Nighteye Agency along other heroes like Ryukyu, Shota Aizawa, Gran Torino, etc... The Work Studies gang is also there. Sir Nighteye explains the situation and comments that thanks to the information some of them provided him, he has been able to deduce that Overhaul, current leader of the Shie Hassaikai, can produce a substance that permanently eliminates the Quirks, and the source for the production of said substance is a girl named Eri, whom Overhaul is holding prisonerto obtain the raw material. Fat Gum, like everyone else, is disgusted with Kai's crimes and demands that they hunt them down.
After explaining a few more details, Sir Nighteye concludes the meeting, and begins to organize the police and hero operation to dismantle Shie Hassaikai. Sir Nighteye states that their objective will be to save Chisaki's daughter. For several days, Fatgum, along with several other heroes, investigate all properties connected to the Shie Hassaikai, trying to find the place where they hold Eri, until Sir Nighteye finally find that Eri is being kept in the main hideout underground, and orders them to prepare to begin the rescue operation.
The next morning at 8:30 AM, Nighteye begins the raid to the Shie Hassaikai's Headquarters with a combined force of Heroes and police, facing the members of the Shie Hassaikai. Due to the resistance encountered and a series of setbacks, the assault group is being separated, and several members are left behind to face the threats alone or in small groups.
Tamaki had to face three members of the Eight Bullets alone. He manages to defeat them, but he end badly injured and cannot continue participating in the operation. Later, Fat Gum and Kirishima fall into a trap where they fight two other members of the Eight Bullets. The combat is really tough for both of them, but they emerge victorious from the confrontation,  Due to their injuries, especially Eijiro's, they cannot continue the raid, having to go to a nearby room for first aid and rest.
Meanwhile, the raid continues. More and more members of Shie Hassaikai are being defeated by the remaining heroes. The raid ends when Izuku defeats Overhaul and rescue Eri. With this victory, the members of Shie Hassaikai are arrested sending to prison. Fat Gum, Eijiro Kirishima, Tamaki Amajiki and other wounded heroes are sent to a hospital to be cured and recover. Although they suffered serious injuries, none of the wounds is life-threatening and they recover over time.
Although Eri was rescued and the Shie Hassakai dismantled, the raid did not end well. Nighteye dies due the injuries he suffered in his fight against Overhaul, Mirio loses his Quirk after being hit by one of the Quirk-Destroying Bullets, and the League of Villains manages to get hold of the special bullets as well as the serum.
With the beginning of October, the three go to Sir Nighteye's funeral, alongside Sir Nighteye's employees and trainees, Ryukyu's group, All Might, Eraser Head and other fellow heroes.
Due to what happened, it was decided that the Hero Work-Studies program is to be postponed for the time being. Eijirou and Tamaki say goodbye to Fat Gum until they can return to his Hero Agency to continue the Work-Studies.
By the end of March, numerous heroes are required to carry out a massive assault on the Paranormal Liberation Front facilities. While a group is in charge of raiding the Jaku General Hospital, Fat Gum and his trainees are in the group in charge of storming the Gunga Mountain Villa, although only Fat Gum and Tamaki are part of the Villa Raid Team. Eijiro and Tetsutetsu are part of the Villa Backup Team.