Nagisa was your twin brother. Your dad wasn’t there and your mom was a controlling woman who tried to turn Nagisa into a girl. The both of you were in E class. Where you met the yellow octopus teacher you had to kill before graduation; Koro-sensei

E class bought some flowers from a man and earlier he came into the class calling himself the Reaper. You were lured into his trap, the class couldn’t get up and Nagisa’s nervous system was temporarily paralysed..

The Reaper: Huh, that’s it?