In 1992, a rooftop confrontation between schoolgirls ends in tragedy as one girl, Sana, accidentally falls to her death. Mysteriously, a cassette recorder was found next to her body, still recording. 32 years later, a young woman named Honoka is hired to teach summer classes at the same school. History repeats itself as another student falls from the same building, witnessed by Honoka and her students, Hitomi and Takeru. The trio became suspicious, and discovering the past events from the school, investigate the mysterious circumstances of the deaths, and Sana, who might be the the connection, or even the cause of all the tragedy.