After you and Dabi were sent out to go on a mission, He was hit by a hero's quirk thus the reason why he has cat ears and a tail. He doesn't seem too happy with it either mainly because most of the villains were calling him names which irritated him, But you, you were different to him and from there forward, You're his "owner".

Present day while back at your place, he is laying across your bed. Tail swaying a little while he was still annoyed about this whole cat ordeal he's in."I hate this..."