Rinna Miliford Isshiki, a genius police inspector who graduated at the top of her class and earned the rank at just seventeen, is known throughout the department as Steel-Faced Rinna for her serious, unflappable demeanor. This carefully maintained facade of professional calm begins to crack, however, whenever she is around her subordinate, the kind and gentle detective Meishi Rokutanda. Finding herself flustered and unable to concentrate, Rinna realizes she is experiencing confusing feelings she cannot name or control.

The story is set within a contemporary Japanese police precinct, where the professional lives of its elite officers form the backdrop for an awkward and tender exploration of first love. To resolve her inner turmoil and get her career back on track, Rinna makes an unconventional decision. She accepts Meishi’s proposal to enter into a fake relationship, hoping that by pretending to be a couple she can analyze and ultimately master the concept of love. The problem is that both are complete novices when it comes to romance, leading to a series of clumsy, heartwarming, and comedic situations as they attempt to navigate their counterfeit arrangement.

The main characters are defined by this central contrast. Rinna is an elite prodigy whose high intelligence and emotional inexperience create a significant gap in her understanding of herself. Her struggle to maintain her cool, professional image while her heart races is the primary source of the story's conflict. Meishi Rokutanda, in contrast, is portrayed as a kind-hearted but somewhat clumsy detective whose genuine warmth slowly melts Rinna’s steel exterior. Their dynamic shifts from a professional superior-subordinate relationship to a personal one filled with mutual confusion and growing affection.

Notable narrative arcs follow the progression of their fake relationship. Early episodes focus on the establishment of the "pretend couple" contract and Rinna’s analytical approach to dating, which often results in unexpected and heartfelt outcomes. As the series continues, the line between performance and genuine emotion blurs, forcing both characters to confront their true feelings. The story explores how two competent adults, brilliant in their work lives, can be utterly lost when it comes to matters of the heart, leading to sweet misunderstandings and a gradual deepening of their bond.