Forty-year-old salaryman Shinichi is a family man with a wife and child, yet he harbors romantic feelings toward his own mother. One day, while the rest of the family is away, he confesses his emotions to her and attempts to pin her down. Initially, she resists, but after persistent persuasion, she reluctantly agrees—only once. The two embark on a secret trip together, telling themselves it's just for this one day. However, their bodies crave each other's presence. Though they intended it to happen only once, they are drawn into pleasure and end up copulating repeatedly. Their relationship, while seeking some form of familial understanding, gradually evolves into both romantic and sexual territory. The resulting inner conflict and shifting emotions deepen the narrative.