Yuu deeply adores her son, and before long, their relationship has evolved into something intimate and romantic. Though living apart, they had long planned a private hot spring trip for just the two of them, and now the day has finally arrived. Reuniting after some time apart, they indulge in an intensely passionate experience. Upon reaching the inn, they immediately head to the outdoor bath, washing each other's bodies while teasing and caressing. Their desire quickly escalates, and Yuu willingly takes her son into her body, enjoying deeply satisfying pleasure together. As they walk down the hallway, a sudden voice stops them in their tracks. It's Yuu's ex-boyfriend, someone she was involved with before meeting her current husband. Shocked, she's unable to resist as he grabs her hand, pulls her close, and begins touching her. Whispering in her ear, he confesses that watching the mother and son's lewd acts in the bath turned him on, and continues his advances. Soon, he exposes himself and forces her into a blowjob. Late at night, while Yuu lies asleep, the ex-boyfriend sneaks into her room, demanding more. Unable to fight back, her most sensitive areas yield to him once again. Thrust after forceful thrust—different from her son's rhythm—drives her to moan uncontrollably as she reaches a powerful climax.