Kazuki returns to his hometown of Amagasaki after six years and reunites with Mayu Koizumi, his childhood friend who now helps run her family's public bathhouse, Yomogi-yu, while also working as an illustrator. Kazuki has been in love with Mayu since they were children, but he never confessed. Mayu recently ended a toxic long-term relationship with a controlling boyfriend who cheated on her, and she has moved back home carrying emotional scars. Soon after their reunion, Mayu makes a startling proposal: she wants to have sex with Kazuki before they start dating, to test whether their physical chemistry works. Her reasoning comes from her past relationship, which convinced her that emotional and physical compatibility are equally essential for a lasting partnership.

Kazuki, still deeply in love with Mayu, accepts the unusual arrangement despite his confusion and anxiety. Mayu has been actively using a dating app to meet other men and evaluate compatibility with them, and she honestly tells Kazuki about these encounters. To understand what Mayu truly means by a good match, Kazuki listens to her detailed accounts of her experiences with several men she met through the app, including Arimura, an overly analytical lecturer who treated sex like an exam, and Iida, a muscle-obsessed man who believed raw physical power was everything. Through these conversations, Mayu and Kazuki openly discuss the nature of compatibility, intimacy, and what makes a relationship work.

A major revelation comes when Mayu discovers that her ex-boyfriend, Yuudai Uno, secretly blocked Kazuki and other male contacts from her phone without her knowledge during their relationship. This explains why Kazuki and Mayu lost contact for years and resolves a long-standing misunderstanding between them. The ex-boyfriend reappears near the end of the first volume, creating new tension and complicating Mayu and Kazuki's evolving relationship.

The story is set against the nostalgic backdrop of Yomogi-yu, a traditional neighborhood bathhouse in Amagasaki, which serves as the central meeting place for the characters. The contrast between the old-fashioned bathhouse setting and the characters' modern, open conversations about sex and dating creates the story's distinctive atmosphere. Mayu and Kazuki navigate their feelings for each other while exploring the question of what it truly means for two people to be compatible in both heart and body.