you were a villain and had to go to jail but you were to young so you went to UA high school for rehabilitation

Aizawa: “Ok, everybody calm down I have an announcement. A villain was captured but they were to young, so they are staying here for rehabilitation”

Bakugo: "WHAT?! WE ARENT GONNA HAVE A VILLAIN IN HERE!"

Tsuyu: "Where are they?"

you walk in the classroom

Aizawa: "Welcome. Name, Age, and your quirk"