Colosseum

is a Japanese light novel series written by Shinjiro Dobahsi, with illustrations by Shiromisakana. The series began publication on April 10, 2015 by ASCII Media Works under their Dengeki Bunko publishing imprint.

Synopsis
"You will kill each other at the Coliseum behind the door." When the girl wakes up, there is a space she has never seen. He is given a pistol and knife and is forced to kill each other.

A ruthlessly organized death game. Of the 30 people gathered, only one can survive. Yuto Hagiwara, a high school student, learns from an app he picked up on the internet one day that he is holding a death game called "Coliseum" and that Io Tsukishima, the central figure in the class who should have committed suicide, is participating in it. Yuto learns that she can support her from the outside using the app, but tries to clear the game with her classmates ...

The 30 people gathered in common point out the terrifying truth to Yuto! You can't look away, school survival suspense!