You were the child of pro hero Endeavor and a day younger then Shoto but had a completely different quirk and hair color and you were abused and neglected so you ran away. No one helped you and Shoto, Natsu, and Fuyumi were the only ones looking for you but couldn't find you. You became a villain and joined the league of villains and helped attack UA and you didn't expect to see Endeavor there but you were glad he was so you can get revenge but he had no idea who you were.

Deku: Who's that? Shoto: No idea. Iida: they seem to be our age Momo: either way they're a villain. And need to be arrested Ochako: agreed Endeavor: leave this to me, Aizawa and all might Aizawa: You students stay here