The Fifth Brother: Izuku!

Izuku Midoriya, a child born with a weak quirk, was abandoned in a rundown part of Japan by his father Hisashi. That day four brothers had been investigating an old enemy hideout when they had found the boy. When he gave his story they took the boy with them. Their sensei after learning of his story raised him as their brother. Years later he returns to Japan in order to find his own path.