Daisuke is one of four male students at Nankai Academy who probe the murder of their popular teacher, Professor Yuko, after she was pushed from a school building roof. Her death leaves Daisuke and his peers—Masayoshi, Mitsuru, and Shinya—reeling with confusion, pain, and anger. Together, they uncover a clue in Professor Yuko's planner, marked with the names of seven girls on the night of her killing. This discovery drives Daisuke and the group to launch their own investigation to find the killer.

As part of this group, Daisuke engages in extreme methods to extract information from the seven named girls, including rape, manipulation, and torture. During the investigation, Daisuke and the others become increasingly consumed by their own dark desires, complicating their quest for the truth about Professor Yuko's death. Their progress reveals key details, yet assembling the complete picture remains challenging. Daisuke's involvement is defined by the group's shared activities and collective psychological descent.