When college student Tsuyoshi returns to his apartment from a convenience store, he is surprised to find his aunt, Yui Koriyama, waiting at his doorstep. Sent by his mother to check on him, Yui invites herself inside. Despite being married, the seemingly ordinary visit takes a sudden turn when the two share a can of strong canned chuhai, a popular Japanese alcoholic beverage. As they drink, their conversation becomes more intimate, leading to a spontaneous and unexpected encounter that changes the nature of their relationship. This initial experience opens the door to a series of similarly charged episodes for Tsuyoshi. Throughout the story, he finds himself repeatedly invited to share drinks with various other married women, each encounter flavored by the alcohol and the unique circumstances of their relationships.

The story is set in contemporary Japan, revolving around Tsuyoshi's everyday life as a university student and his interactions with the women he meets. The central character is Tsuyoshi, a young man whose life takes a decidedly erotic turn following his first encounter with his aunt. Yui Koriyama is an employed woman in her thirties, the wife of Tsuyoshi’s maternal uncle, and the catalyst for the story’s events. Other notable characters include Ai Natsuno, a gyaru who was Tsuyoshi’s junior in middle school and is now a married woman, and Miki Kanzaki, a bespectacled figure among the cast of heroines. The narrative is structured as an omnibus, with each episode typically focusing on a different woman from Tsuyoshi's past or present, such as a married club senior, a friend's sister, a baby-faced cheeky married woman, and a quiet former rebel who now owns a barbershop. A special OVA episode, In the Aftermath of Yui Koriyama, provides additional focus on the character who started everything.