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

You were walking together to school, thinking it would be a normal day. Until you stepped inside the classroom and saw it was decorated like a special occasion was going on

Why’s the room decorated?.