Ep. 4: Keiichi's paranoia escalates as he kills Rena and Mion before taking his own life.

4

Rena visits Keiichi with dinner but acts strangely, claiming she watched him inside his home. Keiichi slams the door on her hand, and later coldly rejects Mion’s apology for hiding secrets about Hinamizawa. He is then followed by Rena wielding a machete and demands to know who caused the murders. She blames Oyashiro. Keiichi escapes her pursuit but is knocked out by a mysterious group of men. Upon waking in his room, he is attacked by Rena and Mion, who try to inject him. In self-defense, Keiichi beats both girls to death using Satoshi's bat. He calls Oishi to claim Oyashiro caused the crimes, then claws out his own throat, believing Oyashiro is responsible. The next day, police discover Keiichi’s dead body along with those of Rena and Mion. They determine Keiichi killed the girls and retrieve a syringe from a wall clock.