Satoru Kido is a 27-year-old Japanese private detective with brown hair, grey eyes, standing 1.77 meters tall and weighing 64 kilograms. He values the personal freedom his profession provides and cultivates a "cool detective" image, frequently seen with a cigarette, which aids his interactions with female clients during information gathering.

Hired to locate the missing ruby-encrusted heirloom ring "Blood of the Phoenix" at the secluded island Nakakouji estate, Kido experiences persistent déjà vu and an unexplained sense of familiarity upon arrival. His assignment involves interacting with the mansion's residents: Ayano (the current mistress), a butler, maid Nozomi, a manservant, and tutor Kaoru. Receiving only vague instructions about guard duties from the butler, Kido independently investigates the family's secrets.

His investigation uncovers that he is the missing Nakakouji heir, explaining his familiarity with the estate. Kido becomes involved in the mansion's hidden activities, engaging in sexual relationships with multiple female residents, including Ayano, Nozomi, and Kaoru, amidst a backdrop of tragedy, love, and hate.

Three months later in a sequel, Kido returns to the rebuilt Genmukan mansion after rescuing Nozomi from the fire that destroyed the original structure. He continues his relationship with Nozomi while confronting lingering secrets tied to his heritage, ultimately achieving closure regarding his family background and relationships.