Keiichi meets Mion's twin sister, Shion; the two are so identical that Keiichi can hardly tell the difference between them. It is also revealed that Mion has a crush on him.

Keiichi's parents leave for Tokyo for a few days. Helped by Satoko and Rika, who makes dinner for him, Keiichi learns about Satoshi, Satoko's older brother, and his mysterious disappearance on the night of last year's Watanagashi.

Keiichi goes over to the Houjou residence to ascertain Teppei's existence and finds Satoko in need of clinical help. At the Furude Shrine, Keiichi discovers Rika's disemboweled body, and Satoko believes that Keiichi is the culprit and flees. After fruitlessly trying to convince her that he is not the murderer, disaster strikes the town of Hinamizawa.

Shion tricks Keiichi in a phone call and later tricks the townsfolk in order to make Keiichi a murder suspect, however she quickly realizes that Oishi suspects her instead. When discovered by Rena and Keiichi, Shion lures Keiichi away and knocks him out in front of Mion. The truth behind the sisters' fate is revealed.