Just like in every other world, the Hinamizawa School club plays games after the classes are over. In this world, Keiichi requests that the club play mahjong. During the mahjong games where he always loses, Keiichi becomes more and more stressed which twists his perception of the events, and he starts to show the symptoms of the Hinamizawa Syndrome. Irie Kyōsuke notices the changes and starts to treat him with the C-120 medicine which prevents the sequence of Onikakushi-hen. However, Keiichi befriends various people through mahjong: Takano Miyo, Ōishi Kuraudo and Akasaka Mamoru. They reveal the history of Onigafuchi and the series of mysterious deaths which worsen his condition. After discovering the deaths of Takano Miyo and Tomitake Jirō on the night of the Watanagashi Festival, Keiichi reaches the Level 5 stage of the Hinamizawa Syndrome which initiates the tragic events of Tsubamegaeshi-hen.