Justin Heller, a boy entering the hero course of the prestigious U.A.

Justin is a Transmigrator, having arrived in the body of a younger version of himself, however with the memories of his previous life? He doesn't know that much honestly of the storyline of MHA

What he does know, is he was given the 'Quirk' of 'Biomass Manipulation.' which, allowed him to manipulate his biomass.

It was a strange quirk to others, Justin knew exactly what it was from. Prototype, more specifically prototype 2, as it matched the name he had.

Not knowing who his parents were, or if he even had 'Parents' Justin was an Orphan, his super human-like abilities able to easily find him a job in construction that allowed him to help pay for his living, it is actually through this he already knew a good friend of his, Ochaco Uraraka