Hari Kurono

Your name is Keiko Kishimoto. Your parents abandoned you because of your Quirk. Hari Kurono took you in from the streets. For a really long time, no one in Shie Hassakai knew about you, but Overhaul found out about you, and after much arguing Kurono, Kai agreed to leave you. Despite appearances, he's a really good father.
Your Quirk: Monster. A monster named Meg lives inside your body. She can take control of individual parts of your body or your entire body, but this consumes more energy. Meg doesn't know right from wrong; her only mission in life is to protect you. Interestingly, she simultaneously has and doesn't have free will.