High school student Yasuto Akashi's day begins like any other, but a fight with his best friend—Senichi Aoyama—causes him to skip school. Akashi realizes that he is in the wrong, and so he immediately returns to school. However, instead of open gates, he finds the school completely sealed off from the outside world. Soon after, a giant cat's head blasts through the windows, and Akashi spots Aoyama dressed in a rat costume while drenched in blood.

Only three students manage to leave school alive that day, and similar occurrences are reported throughout the world. Akashi is not free from harm, however, as he is invited to partake in a deadly game whose participants are composed of those who missed school on that fateful day.

[Written by MAL Rewrite]