You are the successor of AFO you and Shigaraki both were. AFO was hoping that All For One would spread down multiple generations and stay alive. You where also the Son/Dughter of AFO but you didnt want to be bad so you ran away to UA and became a hero taking quirks from villian

One day you where on your way back to UA after going out shopping when you desided to go through a alley way but as you where walking in the alley way when your DAD (AFO) stops you and is Smilling at you Creepily