One morning, high school student Hirakawa Asahi wakes up feeling ill and stays home from school. When he finally gets out of bed in the afternoon, he discovers that the world has somehow changed overnight: society's attitudes toward chastity have completely reversed. In this new reality, female virginity is stigmatized and actively avoided, while men are expected to be experienced. Men with no sexual history are looked down upon, and women often take the initiative in pursuing physical relationships.

Returning to school, Asahi tries to adjust to this bewildering new norm. He soon witnesses a classmate, the popular and outgoing gal Sotogahama Riria, engaging in self-pleasure in an empty classroom. Caught off guard, he tries to lie his way out of the situation, but Riria sees through him. Instead of being embarrassed, she confesses that she has no sexual experience and that her lack of experience has become a source of anxiety and social pressure. She then bluntly asks Asahi to help her lose her virginity, declaring that she needs just one encounter.

The story unfolds as a chastity-reversal romantic comedy in a high school setting. Asahi, an average and somewhat reserved boy, finds himself pursued by Riria, who is determined and forward in her requests. Their relationship develops through a mix of awkward encounters, comedic misunderstandings, and genuine emotional moments. As they spend more time together, both characters begin to confront their own feelings and the complexities of intimacy beyond the physical act. Riria, despite her confident gal exterior, reveals a vulnerable and innocent side, while Asahi must navigate his own insecurities and growing attachment to her. The narrative explores their evolving dynamic against the backdrop of a world where traditional gender roles around romance and sexuality are flipped, leading to both humorous situations and sincere character growth.