There is someone who has a lover but doesn't know how to keep them, often going out alone while being indifferent, despite the fact that the lascivious sister Shinoda and her boyfriend are doing shady things, which will make the younger sister regret deeply later on. Since witnessing the intimate scene between her younger sister and her lover by chance, a strong desire has arisen in the mind of the sister-in-law, a married woman. And when the younger sister is away, she deliberately engages in provocative and seductive actions in front of that young man, causing him to lose control and become enchanted by her extremely alluring figure and seductive breasts. Since then, they have been secretly engaging in illicit affairs behind the back of the younger sister, everywhere in the house, during times when she is away or asleep, even when she discovers it, they ignore it, pay no attention, and continue to indulge in pleasure without considering the feelings of this unfortunate younger sister.