Keiichi Nakagawa works as a police officer at the same Kameari Park Front police box as the protagonist, Kankichi Ryotsu. He hails from an extremely wealthy family, a background that shapes his lifestyle and interactions, providing access to uncommon resources and privileges. This wealth often highlights a contrast with Ryotsu's impulsive nature and financial instability.

Nakagawa possesses advanced linguistic skills, earning him special permission from police headquarters to forgo the standard uniform in favor of his personal attire. This expertise is integral to his duties. He frequently aids Ryotsu during various misadventures, especially when Ryotsu's money-making schemes or inventions spiral out of control. Their dynamic follows a recurring pattern: Ryotsu initiates a venture, achieves brief success, calls on Nakagawa for help as complications arise, and ultimately faces failure as the situation collapses.

Physically, Nakagawa does not significantly age throughout the series, maintaining a consistent appearance despite the narrative spanning decades. Subtle acknowledgments of time passing occur, such as references to the aging of minor characters like Buchao's grandchild. His role remains a stable part of the ensemble cast, characterized by his calm demeanor juxtaposed against the eccentricities of colleagues like the transgender officer Ai Asato. His wealth and linguistic abilities contribute to the comedic dynamic, emphasizing the disparity between his refined background and the chaotic environment of the police box.