Curse of Oyashiro

The curse of Oyashiro, also known as the series of mysterious deaths or S Incidents, is the name given to incidents of death or disappearance that occur on the night of the Watangashi Festival. The legend ascribed to the curse of Oyashiro is that every year, on the night of Watanagashi, one person will die and another will disappear or be "demoned away". It is widely believed in Hinamizawa that the victims of this curse are either directly or indirectly to the supporters of the Hinamizawa Dam Project. A number of people believe that the Sonozaki family is responsible for the incidents, the most prominent believer of this being Kuraudo Ooishi. In order to maintain appearances of power, the Sonozaki family has embraced this suspicion and intentionally acts suspicious in order to inspire fear of the family within Hinamizawa residents. However, the family has nothing to do with the incidents.

The Strange Deaths of Priest and Wife
The strange deaths of priest and wife, also known as the mysterious death of the Furude couple, is the third incidence of the curse of Oyashiro. During the Watangashi Festival, the priest of the Furude Shrine began having heart problems. He was taken to the Irie Clinic but was ultimately pronounced dead from a heart attack. On the same night, the priest's wife went missing. Her slippers and a suicide note were found in front of the Onigafuchi swamp, leading the public to believe that the priest's wife killed herself to appease Oyashiro's anger. In truth, the incident was orchestrated by the Mountain Hounds under orders from Miyo Takano. Miyo had the priest's wife killed as the wife had been attempting to withdraw her daughter, Rika Furude, from the Irie Clinic's study on Hinamizawa Syndrome. The priest was killed to maintain the appearance of one death and one disappearance every year.

The Murder of the Housewife
The murder of the housewife is the fourth incidence of the curse of Oyashiro. During the Watangashi Festival, Satoshi Houjou beat his aunt, Tamae Houjou, to death with a baseball bat. Five days after the murder, Satoshi went to buy a large teddy bear of his sister's birthday and was began to exhibit symptoms of the terminal phase of Hinamizawa Syndrome. Kyousuke Irie took Satoshi to the basement of the Irie Clinic for experimentation and had the Mountain Hounds manipulate information so the murder of Tamae Houjou appeared to have been done by a drug addict. The drug addict was made to confess to the murder and later died by choking on a spoon.

The Fifth Curse of Oyashiro
The fifth curse of Oyashiro changes depending on the arc. Among those who die on the fifth year of the curse of Oyashiro are Jirou Tomitake, Rika Furude, Mion Sonozaki, Satoko Houjou, Rena Ryuuguu, Keiichi Maebara, Teppei Houjou, Kuraudo Ooishi, and Katsuya Kumagai. Miyo Takano occasionally "dies" during this curse, however her death is faked by burning the corpse of a recently deceased woman and fudging the autopsy report.