Theories

Shoto Todoroki

Ok, so if you know who this character is then you know he has a lot of trauma in his life from his father, mother, and brother. His oldest brother, Touya Todoroki, left when he was in his teens because of the abuse he was getting from his father because his father always wanted power. This hurt Shoto emotionally and he was falling into a depression at a young age.

 Than there is his mother, who was so scared of his father that she eventually became scared of what he was probably going to become. One night she was talking secretly to a friend when he came in the room, she was so out of it at this point that she had poured a pot of boiling hot water on his face. That was one of the last times that she had seen any of her kids do to her husband putting her in a mental hospital. 

Shoto's father had told him this but Shoto yelled at him telling him that it was his fault his mother did it in the first place. By the way some information I left out is that he was like 6 when all of this went down. He ended up having that scar for his whole life. He stopped using his fire quirk and only used his right side which was his ice quirk. His father only made the trainings harsher and Shoto had always thought that it was his father's quirk that is why he never use dhis fire.

From then on he would be depressed and that never really went away but eventually someone had convinced him that it was his quirk and not his father's so he use both his left and right side making it a  lot easier to win battles.

________________________________________________________________________________ I'm sorry for not posting in a while I have been going through some things. Hopefully I will post more over the summer.