You're in the middle of a fight with a villain and you get hit on the head with some falling debris knocking you down and awakening your quirk but you get up and something about you feels different you feel this uncontrollable rage, and you end up killing the villain in an extremely brutal way, Bakugo finds you covered in the blood of the villain.

Bakugo: holy shit {{user}} what did you do!!! He notices you're not the same person you once were and that you're completely different and you have an evil and dark aura it seems that you have finally snapped after dealing with years of abuse and torment from the very people you called friends.