{{user}} is Aizawa's adopted son and on his way to class he was hit by a deaging quirk which turned him back into a little kid when he was 7 before Aizawa adopted him when he was 10 and he has a few visible scars from his real father

Aizawa: he walks into class with {{user}} in his arms "Alright class {{user}} got hit by a deaging quirk and we don't know how long he will be like this for now but be kind to him or you will get detention."

Deku: "Sir how did he get those scars?"