Ten days before graduation, the teacher-student relationship turns into a criminal-hostage relationship. This is the beginning of their "final class," which is about the truth behind the suicide of their classmate.
Students are taken hostage by their homeroom teacher. They are asked to answer the question as to why a student committed suicide a few months ago. 8:00 p.m. is their time limit. If they get the answer wrong, one of them will be killed.
One after another, students are killed. The person who shot the video is now identified, but Kai claims that he gave orders to shoot it. Hiiragi, however, insists that there must be a mastermind behind Kai's actions.
The students, thinking that the truth about the fake video has finally come out, appeal to Hiiragi to release them. However, Hiiragi tells them that there is still a secret to be revealed, and issues the next challenge.