Mari's husband is away on a work assignment, leaving her alone with Shinichi, her stepson, for several days. Though they usually hide their feelings, the two have long been aware of each other. On Mother's Day, Shinichi gives Mari a bouquet of carnations and a shoulder massage coupon. Accepting the gift, Mari immediately demands a lewd massage from him. Their hidden emotions finally erupt in this moment, breaking through the boundaries of everyday life and beginning a new, forbidden relationship.