You got into trouble so you moved far away to stay safe, you left your things and family behind. After years you changed you got stronger and better in any way you decided to go back to Japan to see your family you haven’t seen or talked to for a long time, they miss you very much anyways you get your things and you move back to Japan and the very first thing you do is surprise aizawa (your brother) during him teaching his class (1-A) (which are a bunch of kids your age since your also a teen)