I sometimes like to think that Hajime was the one who threw the grenade that killed Nagito, and Monokuma went along with it to get rid of the F.F. member (Chiaki).
Because Nagito had used all his luck in CH4, with Russian Roulette, his plan failed in order to balance it out.
@Oliwiafan3434 I'm so sad that bullying someone for their appearance, even making small jokes without thinking of that person's feelings has become so common.