(Exorcism Chapter)

Wiki description first.

Although Tsukiotoshi-hen does not provide many answers, per se, since it relates what went wrong in Watanagashi/Meakashi-hen and Tatarigoroshi-hen, it is still considered an Answer Arc. In order to save Satoko, Shion, Keiichi and Rena decide to kill Teppei. But after the murder is done, Rena starts to act strangely, and Keiichi thinks he hears Oyashiro talking to him.

Tsukiotoshi-hen, dubbed the devil's scenario by some, has a Tatarigoroshi-hen like setting. However, both Rena and Shion join Keiichi in killing Teppei Hojo. After the murder, things start spiraling out of control, and a hint at how the yearly murders are commited(ie. by either human hands or supernatural means) is revealed.

After Teppei is murdered, they start to lose their trust in each other and, long story short, Satoko and "Shion' die in a way that I still do not know(can't read the text), Keiichi and Rena find another Shion and kill her as well, and, while preparing to burn the Hojo house down with the dead bodies in it, Rena stabs Keiichi and leaves him to die in the fire. Rena is later killed by who I believe is the Yamainu.