Kuraudo Ōishi is a veteran detective assigned to the Okinomiya Police Station who has spent five years investigating the mysterious deaths and disappearances that occur annually in the village of Hinamizawa around the time of the Watanagashi festival. He is approximately fifty-five years old and feels the pressure of his approaching retirement, which drives him to solve the case before he leaves the force. His personal motivation stems from a deep loss: the first victim of the so-called curse was a close friend with whom he frequently played mahjong, and a man who became a second father to him—the manager of the dam construction project—was also killed under suspicious circumstances. Ōishi came to believe that the influential Sonozaki family orchestrated these events, and his fixation on proving their guilt has made him an outsider in the tightly knit community. Many villagers resent his persistent questioning and regard him as a nuisance, and some even whisper that he himself might be the culprit, giving him the ironic nickname of “Oyashiro-sama’s servant.”

In his investigations, Ōishi cultivates informants among the main characters, approaching Keiichi Maebara in particular to extract information about the village’s secrets. His methods are unconventional and sometimes aggressive; he may use charm, subtle pressure, or outright intimidation to get what he wants. While he initially presents a light-hearted, almost playful demeanor, he is capable of becoming menacing and will not hesitate to use violence if he believes it will advance his case. This shift from genial to threatening can inadvertently push the already paranoid protagonists further into distrust and panic, making him an unwitting catalyst for tragedy. Despite his abrasive approach, he is motivated by a genuine desire for justice and a need to understand the truth behind the curse.

Ōishi is rarely seen without a cigarette and typically wears a cream-colored suit jacket over a black collared shirt with a red tie and suspenders. He has a sturdy, muscular build and short grey hair. He is skilled in wrestling and hand-to-hand combat, though he admits he has never fired a firearm. His favorite pastime is mahjong, and he occasionally plays with Keiichi. Later, after retiring, he takes up ballroom dancing to stay fit. His relationship with the villagers is strained, particularly with Mion Sonozaki, who is adamant about her family’s innocence. He also interacts with Mamoru Akasaka, a police officer who becomes a friend and collaborator, and with Rika Furude, whose mysterious knowledge of the repeating tragedies makes her a person of interest.

Throughout Higurashi no Naku Koro ni Kai, Ōishi’s role evolves from a simple investigator into a figure whose actions inadvertently influence the course of events. In the final arcs, he retires and moves with his elderly mother to Hokkaido, but his obsession does not fade. Together with Akasaka, he compiles a written record of everything that happened in Hinamizawa, titled “Higurashi no Naku Koro ni,” hoping that the truth will one day be uncovered and remembered. His development shows a man torn between duty and personal loss, whose relentless pursuit of answers both hinders and aids the struggle against the cycle of tragedy.