Isamu Kenmochi serves as a Tokyo Metropolitan Police homicide inspector. His first encounter with Hajime Kindaichi occurred during the Opera House Murder Case, where Kenmochi appeared dismissive and frustrated over his interrupted holiday, bluntly telling a distraught companion the case "ruined my holiday."

Over time, Kenmochi forged a strong professional partnership with Kindaichi. He frequently acts as the investigating officer on cases involving the teenager, leveraging his authority to facilitate Kindaichi’s unofficial investigations. Despite his own limited deductive skills, Kenmochi fully trusts Kindaichi’s problem-solving abilities, often requesting the teenager’s assistance on challenging cases while promising rewards. In return, Kindaichi relies on Kenmochi for logistical support. Their mutual respect sees Kindaichi affectionately calling Kenmochi "Ossan" (Uncle), and their closeness occasionally leads others to mistake them for relatives.

Physically robust with a black belt in judo, Kenmochi trains junior detectives and maintains extensive law enforcement connections. He demonstrates deep care for family and colleagues, revealing a good-natured personality in later appearances. In anime adaptations, his role sometimes replaces manga-exclusive police characters.

Kenmochi reports to Kengo Akechi, his significantly younger superior. Their relationship remains strained, with Kenmochi frequently irritated by Akechi’s sarcasm and attitude. Despite this friction, Kenmochi acknowledges Akechi’s reasoning abilities.

Across media, Kenmochi’s career advances. By the "Fifth Generation" series, he holds the rank of Chief Inspector in the Tokyo Metropolitan Police Department, continuing his collaboration with Kindaichi and childhood friend Nanase Miyuki. His age fluctuates inconsistently, referenced between 37 and 48 across different cases.