Takagi and Yui have been married for four years. A year ago, Takagi's parents divorced, so he invited his father to live with them. His father is a long-haul truck driver who has a lot of free time and interacts with Yui quite often. He often says vulgar things and touches Yui inappropriately. Although Yui has spoken up to him, Takagi didn't pay much attention, thinking his father was just joking around. One day, when returning home from work, Yui seriously told Takagi that his father had touched her inappropriately and sexually harassed her. At first, Takagi was very angry and decided to move out. However, the curiosity and excitement of knowing his wife was having sex with someone else made him uncomfortable. Takagi discovered that he is a cuckold. He told Yui, and eventually she agreed to this arrangement. Takagi asked her to seduce and have sex with his father again so he could witness it. Despite her hesitation, Yui agreed because she wanted to please him. So, they both went back home, had dinner, and played cards. At that moment, Takagi pretended to be sleepy to secretly observe his wife and father having sex together...