On a night when Yuuji and his wife returned to her parents' home, his stepmother-in-law Yuu welcomed them. Young and beautiful, Yuu was the second wife of his father-in-law, and Yuuji sensed tension in her relationship with his wife. When his wife became upset upon learning of this, Yuuji felt uneasy. That night, as Yuuji headed to the kitchen, he found Yuu drinking alone. When he asked about the strained relationship between her and his wife, their conversation gradually turned toward their sex lives. Carried away by drunken desire, the two crossed the line. That night, as their bodies entwined, they marked the beginning of a forbidden relationship.