Jōichi Kuruma is the self-proclaimed chief detective of the Kuruma Detective Agency. He boldly refers to himself as the Second Generation Sherlock Holmes, although in reality he is widely regarded as a third-rate and incompetent investigator. His hometown is in the countryside, where his family operates a dairy farm called the Himadana Ranch, a detail that hints at a rural background far removed from the bustling city of Washinkyo where the series takes place. His very name is a pun on Sherlock, as the characters for car and lock are combined to phonetically echo the famous detective's name.

In terms of personality, Kuruma is defined by an oversized ego and stubborn pride that far exceed his actual abilities. He refuses to take on cases that do not satisfy his self-image, a habit that has left his agency with no clients for three years and put him three years behind on his rent. Despite his professional shortcomings, he constantly inserts himself into investigations, often making situations worse and earning a reputation as a troublemaker. This negative reputation is cemented when a villain selects him as the Representative of Modern Losers. Physically, he has decent fashion sense but his appearance is marred by several missing front teeth, a condition apparently caused by drinking too much milk. Other characters remark that he would look much better if he did not smile.

Kuruma's primary motivation appears to be the pursuit of glory and recognition as a great detective, though his methods are largely ineffective. His role in the story is primarily that of comedic relief, serving as a foil to the true hero. He runs the Kuruma Detective Agency, which serves as a base of operations. Notably, the agency does not operate legitimately; its daily routine involves using a periscope and hidden microphones to spy on the International Police across the street, using the stolen information to launch their own unsanctioned investigations. Despite his bravado, Kuruma is not entirely without courage, as he is willing to confront enemies or infiltrate bases with only his water pistol and hat, displaying a form of reckless bravery that exceeds that of an ordinary person.

Key relationships define much of his role. He has a rivalry with Toragoro Onigawara, the head of the International Police Agency, and the two frequently clash. His employees include his assistant, Takeshi Yoroi, who is secretly the superhero Hurricane Polymar, and his secretary, Teru Nanba. Teru is also his landlord, a fact that exacerbates his financial troubles due to his unpaid rent. The agency also has a pet, a former police dog named Baron, who is often seen as more intelligent than its owner.

Throughout the series, Kuruma shows signs of development. Though he is oblivious to Takeshis secret identity for most of the story, he eventually discovers that the seemingly useless assistant is actually Polymar. This revelation serves as a turning point, leading to a fresh start as Kuruma welcomes Takeshi back to the agency as the new chief detective. Despite his incompetence, he is not a character to be hated, and he and his agency form a strange but loyal family unit. In a notable event in episode fifteen, Kuruma receives a blue bucket-shaped helmet called the Horamet from a mysterious old woman. Wearing it, he transforms in a dream sequence into a powerful hero named Typhoon Horamar, who possesses powers that even surpass Polymar. This alter ego is later referred to in the final episode when a sleeping Kuruma mutters to himself that he is Horamar.

Kuruma's notable abilities, while often played for laughs, are surprisingly inventive. The pistol he carries is not a real weapon but a deceptive water gun designed to look authentic. He has been known to modify it by adding sleeping pills to its liquid ammunition to incapacitate targets. He also employs his hat as an improvised weapon, throwing it with a surprisingly high degree of accuracy. These skills, though comical, demonstrate that beneath the veneer of a buffoon, he possesses a sliver of resourcefulness that allows him to contribute to the agencys efforts in his own peculiar way.