Kuraudo Ōishi, a detective from the Okinomiya Police Department, relentlessly investigates the annual deaths and disappearances linked to Hinamizawa's Watanagashi Festival. Born November 15, 1923, he is 59 during the 1983 events. His father perished in a Nagoya air raid during World War II. Post-war, Ōishi policed the black market, where he met an older man who became a father figure and later managed the Hinamizawa Dam Project. The manager's brutal murder during the 1979 Watanagashi Festival profoundly impacted Ōishi, fueling his drive to solve the case before retiring to care for his elderly mother, planning to relocate to Hokkaido or Sapporo. Ōishi possesses a rotund, muscular build, gray hair, and green eyes. He frequently smokes Gaster cigarettes. His signature attire consists of a cream-colored suit, black collared shirt, red tie, red suspenders, and dark brown or white shoes; he carries a jacket but seldom wears it. Despite his heavy physique, he is a formidable hand-to-hand combatant, feared as undefeated except by the dam manager. His personality mixes lightheartedness with intense determination. He often chuckles ("Nfufufu"), enjoys mahjong and ballroom dancing, and aspires to become a professional dance instructor by age 80. However, his devotion to solving the Hinamizawa cases leads him to employ morally questionable tactics, including intimidation, coercion, and physical violence. He exhibits particular aggression towards Satoko Hōjō, using force to extract information about her family. Villagers resent his investigations, dubbing him "Oyashiro-sama's messenger" due to the belief that his contact precedes residents' deaths or disappearances. Ōishi suspects the Sonozaki family orchestrates the annual incidents and views the entire village as complicit. Ōishi's interactions vary. He frequently approaches outsider Keiichi Maebara as an informant, though Keiichi later resents his methods. His relationship with Mion Sonozaki is strained by suspicion of her family; cooperation occurs only when mutually beneficial, as seen in Tsumihoroboshi-hen. He holds longstanding animosity towards the Sonozakis over the dam conflict but reconciles with Akane Sonozaki in Matsuribayashi-hen, forming a mahjong group. He maintains friendships with Mamoru Akasaka, Kyōsuke Irie, Tomoe Minai, and Kaoru Yamaoki. Across story arcs, Ōishi consistently provokes paranoia. In Onikakushi-hen, he questions Keiichi about Jirō Tomitake's death, revealing victim connections to Keiichi's friends and exacerbating his distrust. During Watanagashi-hen, he manipulates Keiichi to access the Sonozaki estate, prioritizing the investigation over Keiichi's safety. In Tatarigoroshi-hen, he intimidates Satoko and later ambushes Keiichi to search for Teppei Hōjō's corpse. Himatsubushi-hen (1978) shows him collaborating with Akasaka to rescue a kidnapping victim, detailing Sonozaki influence. By 1985, he and Akasaka investigate the Great Hinamizawa Disaster, compiling findings into the book "Higurashi - When They Cry." Ōishi's actions intensify in later arcs. Meakashi-hen depicts him pressuring Satoshi Hōjō for alibis, while Tataridamashi-hen shows him succumbing to Hinamizawa Syndrome and killing villagers. Post-retirement, he continues investigating the disaster with Akasaka, authoring the book to ensure the incidents are remembered. His final appearances involve reconciling with former adversaries and persisting in his pursuit of truth beyond police work.