It was orchestrated by this girl, Enoshima Junko... who went to Hope's Peak. Ours wasn't the first mutual-killing incident, it was the third.

The first was one at Hope's Peak. She forced the student council into it, as well as another student. The scientists at Hope's Peak had been researching and working on a project that could make an ordinary person into a genius though brain surgery... that student murdered most of the student council.

[Absently, his hand raises to skim across his forehead, kneading against his temples.] The school tried to hide this, but Enoshima spread it to the reserve course students. They were students without talents, who paid to attend Hope's Peak, but were still treated like second-class students.

Enoshima... used them. She and the others she had with her, people she'd brainwashed, who she made to give into their despair called Super High School Level Despair. With her influence, the reserve course students rebelled, protested, and their social unrest spread outside of the school... Eventually, whatever purpose behind it was lost. It was just pure war.