When his wife refuses to let him have sex because she is tired from raising her child, Kazuki comes to a box health club, where he bumps into Kana, a beautiful mom friend from his son's class. It gets awkward, but she gently helps him out, saying, "It's our little secret, okay?" He feels guilty, but the sense of immorality and excitement of his wife's mom friend helping him out wins out, and he ends up visiting the box health club again.