Machi Isono is an intelligent criminologist who operates a private consultancy firm. She previously worked for the Japanese police before resigning to establish her own agency, the Isono Agency. A red-haired young woman, she is confident and determined in her endeavors. Upon learning of Kazuhiko Amamiya’s release from prison, she employs him as a consultant and invites him to reside in the large apartment that serves as both her home and the headquarters of her business, which she shares with her younger sister, Miwa Isono. Her role in the story centers on investigating the dark conspiracy surrounding the Gakuso organization and the programmed personalities tied to the historical serial killer Lucy Monostone. She uncovers that the personalities of Amamiya and Shinji Nishizono are genetically and psychologically engineered, and she later learns that her own sister carries a copy of one of these personalities. Her motivations are driven by a desire to understand and expose the truth behind these crimes, as well as to protect those close to her. Key relationships include her professional and personal bond with Amamiya, her protective connection to her sister Miwa, and her adversarial link to Gakuso. Throughout the series, she evolves from a former police officer running a small firm to a central figure in unraveling the overarching plot, with her real name eventually revealed as Wakana Isono Monostone. Her notable abilities include advanced criminological knowledge, psychological profiling, and sharp investigative skills, which she employs to navigate the complex web of multiple personalities and corporate manipulation.