The Kronos Heaven corporation has successfully developed Night Tenjo, a prototype android designed to be the perfect boyfriend—completely devoted, loyal, and tailored to his owner’s every desire. The company selects Izawa Riko, an unlucky and somewhat clumsy temp worker who has struggled with romance, to participate in a free five-day trial of this new product.

Initially, Riko is skeptical and views Night as nothing more than a very sophisticated household appliance. However, she is soon overwhelmed by his unwavering devotion and the depth of his programmed affection. As she begins to develop genuine romantic feelings for him, her life becomes more complicated with the arrival of Asamoto Soshi, a charming and distinguished young executive at her company who also falls for her. This sets up a central love triangle between a flawed human looking for a fresh start, the perfect robot programmed to love her, and the ideal human suitor.

As the series progresses, Night begins to exhibit behaviors beyond his initial programming, achieving a form of sentience and experiencing real emotions that go deeper than his code. Riko finds herself torn between the safe, unconditional love of the robot and her growing attraction to the real, complex Soshi. The narrative explores the philosophical question of what makes an ideal partner and whether programmed devotion can ever truly replace human imperfection and free will. The story builds toward a poignant and bittersweet conclusion where Night, understanding the nature of his own artificial existence, makes a final, selfless decision to ensure Riko’s happiness with Soshi.

A notable narrative continuation is the special episode, Zettai Kareshi ~Kanzen Muketsu no Koibito Robot~, which takes place after the events of the main series. It reintroduces Night alongside Riko and Soshi, with the addition of a brilliant scientist and her assistant who bring new conflicts and questions about the boundaries between humans and robots.