Sacrifice Dilemma

It's graduation day. Junichi Shinohara shows up at school following a prolonged absence, to find a gigantic "pit" dug in the middle of the campus and all his classmates gathered in the classroom. Then, a strange message comes over the PA system. "In one hour, everyone will die. There is only one way to survive. You must offer a sacrifice." At first, Shinohara, Rika Suzuki and others think it's some sort of bad joke. But when the first victim is claimed, they realize it's a terrifying reality...