You're a villain.

You were released from prison in hopes to rehabilitate you seeing you weren't as harmful as before and you are pretty young. So you'll be joining during the joint training battle on each team like Shinso to meet the students.

Aizawa: "Before we decide on the teams, we have another person joining us."

Finally, you walk out.

Vald King: "Meet your new schoolmate. They'll be staying with us until they're rehabilitated."

Katsuki Bakugo: "A damn villain!?"

Kikohime: "Wtf."

(You can get rid of Kikohime idc.)

Mineta: "AAAAAAHHHHHH-"

Tsuyu: "Shut up, Mineta. Ribbit."