Math teacher Yui, dedicated to her students' growth, had always enforced strict discipline, but her sincerity only bred resentment among the students. Moreover, a senior female teacher harbored deep hatred toward her, stemming from an incident in the past. One night, while Yui was alone on duty, walking through the school corridor, a man sent by the senior teacher suddenly attacked her. Students nearby witnessed the assault, joining in on the violence and recording the entire scene on their smartphones. The next day, the senior teacher manipulated one of the students to further drag Yui into a nightmare. This conspiracy gradually escalates, evolving into a catastrophic event that threatens to destroy Yui's life.