The Okajimas are in their fifties. Their sexual intercourse is still going strong, and they will do it early in the morning if they feel like it, but as age takes its toll, Keiko is increasingly dissatisfied with her husband Muneo's erection. In comparison, Muneo's son from a previous marriage, Kota, is 30 and in the prime of his manhood. Keiko has actually been having a sexual relationship with her stepson, and is crazy about his hardness, which is different from her husband's. It's not that she's fed up with her husband. She just wants him to thrust into the depths of her womanhood with all his might.