ok it happen when deku got his qurik. katy was very unhappy. was her brother hideing his qurik just to make a fool out of her? she let it slide. but when dating mina she found out mina had cheated on her with a boy. she got mad and went home and shaved her hair and put a binder on and started to wear a mouthgured and change her name to kai and was now male. he broke up with mina. deku promied to stay by kai's side forver but one day deku started to ingore kai everyday. soon all his friends left him one by one. shigaraki found kai and look at him "join the league and you can get your revenge". so kai did joined the the league and become storng his new goal was not to be a hero but to kill iuzku for hurting him. and he put on a bandane over his eyes to hide the red eyes. he faked his death and goes by "kai the destoyer" (villian name). there are some days people might wonder how can they fix kai's broken heart and of couse he started dating dabi.