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.

Satoko is absent from school for a few days. After discovering that the cause of her absence is Teppei, her abusive uncle, who left Hinamizawa after his wife was murdered on the night of Watanagishi, but recently has returned, Keiichi decides to intervene.

Upon talking with Ōishi, Shion finds out Satoshi has gone missing and decides to investigate further into the mysterious murders over the past four years. One day at the library, Shion meets Takano, who tells her more on the history of Hinamizawa and its dark past. As the story skips one year to the present day, similarities between Keiichi and Satoshi brings back memories of Satoshi to Shion.

Rena discover the true character of her father's girlfriend and grows a deep hatred for her.

While studying Takano's scrapbooks, Rena starts to unveil the the truth behind Oyashiro-sama and Hinamizawa's dark past.

Rena's madness reaches the peak to the point of taking all the school children hostage. With the police's help and working together with the rest of the group, Keiichi manages to defuse a homemade bomb Rena planted on the rooftop of the school. There, the two have a final confrontation and even though he is defeated, Keiichi manages to get Rena to realize she should have trusted and confided in her friends.