Chief Tanaka serves as a police chief within the Tokyo Metropolitan Police, privy to the highly classified 8-Man project. He possesses extensive law enforcement experience and shares a complex, strained history with Detective Hazama, who later becomes the cyborg 8-Man. Tanaka vividly remembers Hazama's past actions, including an incident where Hazama killed seven men—three of whom were corrupt police officers—and a separate chase involving a criminal named Tony Glek. This history fuels significant tension whenever their professional duties force them together, making Tanaka resent the necessity of collaborating with Hazama again.

After Hazama suffers near-fatal injuries, Tanaka reluctantly agrees to Dr. Tine's radical proposal to transfer Hazama's consciousness into a cyborg body, despite initial reservations about the concept's extremity. This decision results in Hazama's transformation into 8-Man. Following 8-Man's return to active duty, Tanaka publicly feigns ignorance about the cyborg's identity and origins while privately coordinating with Dr. Tine to safeguard the secret. He observes and acknowledges 8-Man's enhanced effectiveness in combating crime compared to Hazama's earlier conduct, though privately harbors curiosity about specific incidents, such as an event at a stadium, which Dr. Tine later clarifies.

The spelling of Tanaka's name and his specific role vary across adaptations. In the original Japanese manga and anime, he is consistently depicted as "Chief Tanaka." However, the English-dubbed version of the anime renames him "Chief Fumblethumbs." His character development culminates in a grudging recognition of 8-Man's contributions, particularly in resolving major cases. Despite his initial animosity toward Hazama, Tanaka ultimately credits 8-Man's efforts as pivotal in clearing complex investigations.