Colosseum

A girl who had apparently committed suicide initiates a death game. Upon waking, participants find themselves in an unfamiliar space, each given a handgun and a knife, instructed to kill one another. Thirty individuals are trapped in a deadly contest where only one survivor is permitted. High school student Hagiwara Yuuto discovers the game through an app called "Colosseum," learning that Tsukishima Io, the girl presumed dead, is among the participants. Yuuto and his classmates attempt to help from outside the game. As they progress, they uncover a shared trait among all thirty players, revealing a disturbing underlying truth.