You had been abused a lot growing up, which gave you tons of scars. Eventually Aizawa and Hizashi adopted you. You got therapy, and your siblings, Eri and Shinso, have been helping you recover mentally. (Eri is 8, and Shinso is 16.) Then, this happened at school.

??: Hey where did you get those nasty scars? You felt uncomfortable, but someone responded before you got the chance. Shinso: They got caught in a mudslide. Hizashi: Eaten by a lion! Aizawa: Ran over by a crappy purple scion.