Narutaki is the son of the greatest detective in Steam City, a metropolis powered entirely by coal and steam. Orphaned as an infant when a mysterious man killed his parents, he was raised by the loyal family butler Kawakubo and later took up his father’s mantle as a private detective. Despite his young age, Narutaki is regarded by many as a child prodigy, though his earnest energy can strike some as an annoyance. He is deeply compassionate and sometimes naive in his dealings with both the citizens he protects and the criminals he pursues, believing in the possibility of redemption even for his worst enemies. His overriding motivation is a fierce love for Steam City and a solemn vow to defend it from the villains who exploit its thick, concealing fog for their schemes.

Narutaki serves as the central protagonist of the story, heading the Narutaki Detective Agency. He works closely with the Steam City police, particularly Inspector Yagami and Detective Onigawara, often providing the deductive insight that the authorities lack. His closest allies are his nurse-assistant Ling Ling, whose mechanical expertise and loyalty are invaluable, and Goriki, a large, steam-powered megamaton robot that acts as the team’s muscle. Goriki was built by Ling Ling’s father and operates autonomously, setting it apart from other remote-controlled megamatons. Narutaki’s key relationships also include a rotating rogues’ gallery of adversaries: Phantom Knight, the vengeful son of the man who killed Narutaki’s parents and his most personal arch-nemesis; Le Bread, a masked criminal mastermind who sees Narutaki as his equal and rival; the jewel thief Crimson Scorpion; the mad scientist Dr. Guilty; and the machine-obsessed Machine Baron.

Over the course of the series, Narutaki shows development through his encounters with these villains, each case testing his ideals and forcing him to confront the darker aspects of his past, such as the truth behind his parents’ murder. He remains a sober and intense young man, but his experiences deepen his resolve and his bond with his team. In terms of notable abilities, Narutaki possesses no superhuman powers but relies on above-average agility, keen observational skills, and a deductive method reminiscent of classic literary detectives. He carries a multi-purpose three-shot pistol with a wide array of attachments, including a chaff bullet, drill, wrecking ball, fire extinguisher bomb, and grappling hook. He also uses a steam-powered motorcycle, a bulletproof coat, and numerous smaller gadgets such as a camera ring, disguise stickers, an electronic mail device, and homing transmitters. Off-duty, he has a taste for very strong coffee and a passion for building toy models, small touches that round out his character without diminishing his dedication to justice.