As the school year draws to a close, Kenta and the others enter the derelict building after receiving identical mysterious notes. Once the entrance is sealed from outside, unease spreads quickly among the group as they search for an explanation and a way out. Rika disappears without warning, leaving behind only a cryptic recording that deepens the sense of dread. The remaining students and teacher must confront rising suspicions while piecing together the intent behind their isolation.