Naoto Tamura, a detective at the Central City Station, is a cyborg secret investigator of the Metropolitan Police Department. His rank is Assistant Commissioner. Although he is a cyborg, it seems that he can live a life that is not much different from that of humans.

The body is made of Jiban Fiber, and is almost impervious to most firearms. Has the force to lift a steel frame, and the speed is comparable to thoroughbred. Jiban's power is electrical energy, which is unsuitable for long-term battles, & he has almost run out of energy. Also, although he excels in shooting, it is hard to say that he excels in swordsmanship.

Jiban usually lives as a direct person (Naoto's identity) and freely transforms into a Jiban as needed. The details of this transformation process are hardly mentioned in the series, and the clear transformation scene itself throughout the whole story also started as Jiban for the first time when transforming using his Electronic Notebook in Episode 10.