Back in June 1983, the club participates in a game of "zombie tag". On their way home, they run into Irie, Tomitake, and Takano, who tell Keiichi about the yearly murders known as "Oyashiro-sama's Curse". However, he understands why his friends hid it from him and doesn't resent them for it. Regardless, this fails to reassure Rika, as she grows progressively depressed as the day of the Watanagashi Festival approaches.

In order to save Satoko, who is terminally infected with the Hinamizawa Syndrome, Rika offers herself as a test subject for Irie and Takano's research. More light is shed into the deaths of Satoko and Rika's parents, and its involvement with the legend of Oyashiro-sama's curse.