It was one little thing that pushed Izuku over the edge. One tiny change that brought his situation to Nezu's attention. One single visit from a hero to his middle school that changed everything.
Izuku stops dyeing his hair, and when it returns to its natural color All Might notices some similarities between his successor and a certain villain.
(I'm not great at writing descriptions, just read the book. I promise it's a lot better than whatever this is.)
I do not own BNHA or any of it's characters.