Brothers' bride swapping - Bold swapping in front of father-in-law -

Brothers (older brother Ginji and younger brother Hiroshi) and their wives Miwako and Misa gather at their parents' house for the long holidays. My father-in-law, Kiyoharu, lived in my parents' house, but he had recently started suffering from dementia, so we gathered together out of concern. However, while the couple was spending the holidays relaxing, behind the scenes each of them was having mixed feelings as a man and a woman. Hiroshi continues to have feelings for his brother's wife, Miwako, and Hiroshi's wife, Misa, is attracted to Ginji. The couple had a repeated affair, but their father-in-law's random actions tore apart their relationship...