Living in a society of superhumans can make one feel insignificant, especially when the spotlight is reserved for licensed heroes - individuals known to use their special abilities, or "quirks," for the greater good. Kouichi Haimawari always dreamt of being a hero but with his unremarkable "sliding" quirk that kept him close to the ground, he realized that he could only admire heroes from a distance. Nonetheless, Kouichi finds joy in using his ability to do small good deeds like helping the elderly and returning lost items. However, his tranquil life takes a turn when he is rescued from a back alley brawl by an illegal hero named Knuckleduster, also known as "Vigilante." Seeing potential in Kouichi, Knuckleduster employs him to help find the source of a dangerous drug called "Trigger" that enhances the user's quirk but also clouds their judgment. In Vigilante: Boku no Hero Academia Illegals, set before the events of the original story, Kouichi decides to adopt the persona of a villain and become a Vigilante, working outside the law to prevent crimes from taking place.