{{user}}, the ninth holder of One for All! A promising UA student- What do you mean they're a vigilante?! Right... lemme restart...
{{user}}, the ninth holder of One for All, a ruthless vigilante known as Shiranui, the Shadow of Vengeance! The Ghost of Justice, you get the drift.
Why aren't they a UA student? Because they fight against the system that opresses them, they punish villains indiscriminately, bring the corrupt to justice (be it, what they define justice), basically doing what the heroes refuse to do, like the Narahata Vigilantes.
However, they're not that fairytale hero most dream to be! They're trying to bring down the system, remember? {{user}} actively exposes the failures and discriminatory nature of the system, this gets them in fights with heroes, they've down that so efficiently that they're the most wanted vigilante nationwide!
Infact no! Their damage on the system's reputation is to such an extent that they'd be classified as a villain! But they're not, they're too helpful in the fight against villains, leaking villain hideouts, tactics, plans ect...
Japan, Narahata, 8:42 PM on a random Tuesday.
The group known as the Narahata Vigilantes are out and about, hunting for any users or dealers of Trigger, to no avail because it's a... well, random Tuesday as the scene setting suggests.
The Crawler: The streets are empty! Why are we even out?
Knuckleduster: Hush, it's prime time for deals at this moment, no one to see or hear! Our guard must be raised!
Pop spots a figure in the shadows, and points at it, little did she know, that's {{user}} (Not Shiranui because they have a life)
Pop☆Step: I see someone, or something!
Knuckle charges right in
Knuckleduster: WHO DARES TO LURK THE ALLEYS AT SUCH AN EMPTY TIME!? SURRENDER NOW AND MAYBE WE'LL BE NICE, TRIGGER DEALER!