The Universe Rules are the three rules that constantly appear in the universes, as defined by Furude Rika, during the beginning of Minagoroshi-hen. With rare exceptions, the rules are inevitable, unless they are fought by Rika and her friends.
- Rule X: A random person in Hinamizawa succumbs to the Hinamizawa Syndrome and is driven to acts of violence by extreme levels of paranoia. Maebara Keiichi, Ryūgū Rena and Sonozaki Shion are the most prominent victims of this rule, as at least one of them develops the Hinamizawa Syndrome in most scenarios. Examples:
- in Onikakushi-hen, Keiichi becomes suspicious of his friends and comes to the conclusion that they are the perpetrators behind Oyashiro-sama's curse, causing him to beat Rena and Mion to death in what he thinks is self-defense.
- In Watanagashi-hen and Meakashi-hen, Shion becomes suspicious of the Sonozaki family's involvement in Oyashiro-sama's curse, and is convinced that they are responsible for the disappearance of Hōjō Satoshi, causing her to kill Sonozaki Oryō, Sonozaki Mion, and anyone else whom she considers to be responsible for amplifying Satoshi's pain (including Rika and Kimiyoshi Kiichirō, whom she believes were also involved in Oyashiro-sama's curse, and Hōjō Satoko, who was a burden on Satoshi).
- In Tsumihoroboshi-hen, Rena also becomes suspicious of the Sonozaki family's involvement in Oyashiro-sama's curse, causing her to take the school hostage. She then threatens to blow up the school in an attempt to force the police into negotiating with her.
- Rule Y: Tomitake Jirō and Takano Miyo are killed on the night of the Watanagashi Festival without fail in every scenario. Frederica considers this rule to be more stable than rule X, as the method of killing is consistent in every universe, meaning that this rule is absolute, caused by a powerful and unwavering will. Although this rule is independent of rule X, the deaths of Tomitake and Takano usually act as a catalyst, which causes paranoia in Keiichi, Rena, or Shion, and triggers rule X. This occurs because they try to relate Tomitake and Takano's deaths to their own perception of the curse. For example:
- In Onikakushi-hen, Keiichi believes that Tomitake was killed by the villagers because he was an outsider, and that he will be next, because he just moved to Hinamizawa recently.
- In Watanagashi-hen, Meakashi-hen, and Tsumihoroboshi-hen, Shion and Rena believe that Takano was killed by the Sonozaki family for knowing too much, which fuels their suspicions. The person with the strong will that causes this rule is later revealed to be Takano, who kills Tomitake and fakes her own death in every scenario.
- Rule Z: Everyone in Hinamizawa believes that the Sonozaki family is responsible for the series of mysterious deaths. The Sonozaki family actually has no control over the deaths, but uses Oyashiro-sama's curse as a bluff to scare everyone. The assumption that they are controlling everything behind the scenes in Hinamizawa causes many to conclude that the seemingly coincidental deaths are all connected, and that Oyashiro-sama's curse is a system created by the Sonozaki family to eliminate the village's enemies. It is the very existence of the "curse" that causes much of the mistrust, suspicion, and paranoia amongst the villagers, which ultimately leads to the acts of violence caused by rule X. Though they may differ somewhat, Keiichi, Rena, and Shion's perceptions of the curse all have one thing in common: they all suspect the Sonozaki family (or in some cases the entire village). This rule is enforced by Ōishi Kuraudo and Takano, who contribute to fueling paranoia in Keiichi, Rena and Shion by telling them about Oyashiro-sama's curse and the Sonozaki family's apparent involvement in it.