Kareshi ga Iru no ni centers on young women who already have steady boyfriends yet find themselves drawn to other men. The narrative explores the emotional friction between loyalty to an existing partner and the unexpected pull of a new attraction. The series is structured as an omnibus, meaning each chapter or story arc follows a different protagonist in a similar predicament, though all share the core theme of infidelity and emotional turmoil.

The first chapter introduces Tamayo, a member of her schools literature club who is in a stable relationship. Her life takes a complicated turn when she attracts the persistent attention of Eidaka, a younger underclassman. Unlike typical romantic comedies where the heroine might be single and available, Tamayo already has a boyfriend, making Eidakas advances a genuine source of internal conflict and guilt rather than a simple courtship.

The setting is primarily a Japanese high school environment, using familiar locations like classrooms and club rooms to heighten the tension between public normalcy and private emotional chaos. As the series progresses through its omnibus format, each new story likely shifts focus to a different female lead and the specific man who disrupts her committed relationship. These arcs presumably explore different facets of the same question why someone who claims to be content with their partner would risk that security for a fleeting or forbidden connection. The tone leans into psychological drama, examining the justifications and rationalizations people create when navigating the gray areas of romance and commitment.