Hitozuma chijô: Shitoyakana seikô

Original title: 人妻痴情 しとやかな性交

Naoya works for a top company, owns the house his deceased parents left him, has a beautiful wife, and enjoys a harmonious marriage. He's at the height of happiness, unable to ask for anything more. However, misfortune strikes suddenly one day. Naoya experiences excruciating pain in his heart while at the peak of intimacy with his wife, Marie. Soon after, Naoya is forced to stay home and recover. In stark contrast to the depressed Naoya, Marie is flirting with insurance salespeople and newspaper solicitors, even using lewd jokes... Naoya becomes suspicious of his wife's change. Then, his wife's younger sister, Haruka, enters the house with a man...