Mirko's Team vs. Takeshi Bushijima

Mirko's Team vs. Takeshi Bushijima is a persecution in which the heroine Mirko along with her T.U.M. trainees Deku, Uravity and Katsuki try to catch Takeshi Bushijima, responsible for releasing a toxic fog.

Prologue
Izuku, Ochaco and Katsuki carry out their first Team Up Mission under Mirko, although the heroine is not very interested in them. During their patrol, Izuku meets a hooded boy who is envious of the heroes since they can freely use their Quirk. Izuku notices that he looks pale, but the boy asks him not to approach him, and leaves. Izuku and the others return to the hotel that Mirko uses as a temporary base.

In a dark alley, the boy begins to feel unwell and needs to use his Quirk, leaking out a toxic fog which spreads across the Sarumai District, affecting many passers-by. People try to escape as they can from the place, and the news soon reports the incident, notifying that the person responsible is a Takeshi, whose Quirk is Poison Gas. Izuku recognizes him as the boy he met before. Mirko and her “team” decide to face him.

Battle
Equipped with gas masks to protect themselves from poisonous fog, the heroes arrive at Sarumai district, where people flee desperately not to be intoxicated. While Mirko rescues the stragglers, Izuku uses the One For All to shoot a wind pressure to keep the venomous fog from spreading further, causing it to disperse enough to allow Ochaco to float in midair with his Zero Gravity and scope where the gas source is currently coming from. Ochaco spots Takeshi heading for the edge of town.

Katsuki immediately launches in his pursuit, being closely followed by Izuku. Izuku finds Takeshi's behavior strange, as he seems to avoid crowds of people, and wonder what he wants. Katsuki replies that he is just someone envious who wants to free his Quirk. Takeshi is about to leave the alleys, but seeing that there were too many people at the streets, he takes another passageway, leaving Izuku confused on his intentions.

Using his Explosion Quirk, Katsuki manages to overtake Takeshi by jumping off the walls of the surrounding buildings, blocking his path. Takeshi tries to back off but soon Izuku, Ochaco and Mirko appear to surround him, the Rabbit Hero proclaims that Takeshi is wrong if he thought he could escape from four heroes, and Katsuki leaps on him. Izuku finally realizes what issue is affecting Takeshi, and stops Katsuki before he can land a hit on him.

Katsuki questions Izuku for helping Takeshi, but Izuku corrects him saying that Takeshi's not a bad person at all, as he has been purposely avoiding crowds of people. He doesn't want to cause any harm at all, but he just unable to suppress his poison Quirk. Takeshi tells them it's true. His quirk creates a poisonous gas that builds up inside him, and he has to release it every once and a while if he doesn't want it to destroy him. However, with the current laws, he would be classified as a villain if he does it.

Katsuki understands the situation and decides to help Takeshi with his problem. Mirko is still cautious concerning the idea of helping someone whom she considers a villain, but seeing that Izuku and Ochaco trust Katsuki allows him to continue. Katsuki orders Takeshi to release all the gas he has accumulated over the years. Takeshi is worried about using all of his dangerous Quirk but Katsuki yells at him to stop talking and just do it. Izuku takes off his gas mask and asks Takeshi to trust them, reassures it with a confident smile.

Katsuki ask Ochaco to float Takeshi and himself as high as possible. Izuku says that being a hero is not about beating villains but about helping people who are in trouble. Takeshi releases all the stored Poisonous Gas while Katsuki burn away all the gas with his explosions. Then, Ochaco returns them to the ground safelly. Feeling much better, Takeshi takes off his hood, and crying with happiness, thanks everyone for helping him, hugging Katsuki to his displeasure.

Aftermath
Takeshi is arrested by the police because the gas that did escape while he was fleeing the heroes incapacitated several people. Fortunately for him, Mirko's team explained the whole situation, and when its reported by the news, many citizens were understanding and signed a petition to shorten his sentence.