"Zettai Kareshi" is a manga series that blends romance, science fiction, and drama. The narrative centers on Riko Izawa, a young woman working at a confectionery company, who struggles with loneliness and self-doubt. Her life takes an unexpected turn when she wins a humanoid robot named Night Tenjo through a mysterious lottery. Night is designed to be the perfect boyfriend, programmed to fulfill Riko's emotional and physical needs. As Riko and Night grow closer, their relationship evolves beyond his initial programming, exploring themes of love, humanity, and the boundaries between artificial intelligence and genuine emotion.

The story delves into the complexities of their bond as Riko grapples with societal expectations and her own insecurities. Night, despite being a robot, begins to exhibit human-like emotions, raising questions about the nature of love and identity. Their relationship faces challenges from external forces, including Riko's childhood friend Soshi Asamoto, who harbors feelings for her, and the corporation that created Night, which seeks to reclaim him for their own purposes. The tension between Riko's growing affection for Night and the ethical dilemmas surrounding his existence drives much of the plot.

The manga also explores the lives of secondary characters, such as Soshi, who struggles with his unrequited love for Riko, and Night's creator, who grapples with the moral implications of his invention. The interplay between these characters adds depth to the narrative, highlighting the emotional stakes and ethical questions at the heart of the story. "Zettai Kareshi" balances lighthearted moments with poignant reflections on love and humanity, creating a compelling and thought-provoking tale.