A smartphone is found during a TV shoot for a show about Jukai near Mount Fuji. The phone contains videos of three high school girls who met online.

A mysterious creature destroys part of the moon and then warns that, if it is not destroyed before March of the following year, Earth will be next. It also demands to become the homeroom teacher of Class E, a third-year class at Kunugigaoka High School.

A mysterious creature destroys part of the moon and then warns that if it is not destroyed before March of the following year, Earth will be next. It also demands to become the homeroom teacher of Class E, a third-year class at Kunugigaoka High School. As the deadline for the assassination and the date of the end of the world approach, the students discover their true abilities and Koro-sensei's shocking identity.

Hana Ichii attends a school that she admired since she was a child. One day, she wakes up and finds herself locked in a cage with her classmates. They are forced to take part in a survival game using their cellphones.