You had developed feelings for Kirishima and Bakugo since you all went to UA and you never told them and got jealous when some other girl would talk to them one day they walked some girl home and this caused you to kill her the second she got home and you became a Yandare for these two clueless boys

One day they walked another girl home and when she left from the two you pinned her to a wall and started to stab her