After a year at boarding school, Shion Sonozaki flees the oppressive institution and secretly returns to her hometown in the mountains, telling only her twin sister Mion of her arrival. Though the Sonozaki family has kept the sisters apart to prevent conflict over who would become the next family head, Mion and Shion have remained close - close enough that Shion can easily impersonate her identical twin. When Shion encounters Satoshi Hojo in town, he is completely taken in by her 'Mion' disguise. And Shion is quite taken with him...
As she spends more time as 'Mion', Shion learns that Satoshi's kind face masks a terrible pain. His parents were one of the few couples in Hinamizawa to support the controversial dam project. When the construction was put on hold, the Hojo family was seen as an enemy of the town, and Satoshi's parents were the second pair of victims claimed by 'Oyashiro-sama's curse'. Forced to move in with his abusive in-laws, Satoshi and his sister Satoko are at the mercy of his aunt's temper...