Project sentry

When he was five Izuku was take, abducted, given away by his family, they don't know. But he was there, in hell on earth.

Stuck in there for five years, experimented on, prodded, probed, he was changed fundamentally and physically.

Until one day, the place he was being held was raided, and he was saved. But his time there would haunt him for the rest of his life.

Nezu. Seeing what they did to the boy, both mentally and physically, decided the school would take him in.

Nemuri Kayama and Shota Aizawa, legally and figuratively became Izuku's parents.