One year ago, Natsumi Kimiyoshi and her family moved away from the mountain town of Okinomiya. According to local superstition, those who leave Okinomiya or the nearby village of Hinamizawa will be cursed by the god Oyashiro. However, everything has been peaceful and quiet since they moved—that is, until gas suddenly erupts from the swamp near Hinamizawa, killing thousands of people. Unbeknownst to Natsumi, this "Great Hinamizawa Disaster" would serve as the catalyst for countless unspeakable tragedies in the days to come.

After the disaster, many of Hinamizawa's former residents, such as Natsumi's grandmother, begin to act very strangely. In order to stave off what she believes is Oyashiro's curse, her grandmother begins plastering talismans all over their house and drowning puppies in order to appease the god. These erratic and horrifying actions leave Natsumi and her family fearful for their lives, leading Natsumi's mother to do the unthinkable...