Kuraudo Ooishi is a veteran Okinomiya detective obsessed with investigating deaths and disappearances tied to Hinamizawa's Watanagashi Festival. His drive to prove the Sonozaki family's guilt originates from the lynching and dismemberment of his father figure, a dam project manager opposed by villagers and considered the first victim of Oyashiro-sama's curse. Villagers distrust Ooishi for his aggressive tactics and proximity to victims, ironically suspecting him of being "Oyashiro-sama's messenger." He is a muscular yet overweight elderly man with short grey hair, green eyes, and a habitual chain-smoker, typically wearing a cream suit with suspenders. Ooishi shifts between lightheartedness and intimidation, employing manipulation or violence in investigations. His interactions with protagonists like Keiichi Maebara often worsen their paranoia about village conspiracies. He eventually retires and relocates with his elderly mother but continues investigating the Great Hinamizawa Disaster alongside Mamoru Akasaka, compiling findings into the book *Higurashi no Naku Koro ni*.

In the intersecting *Rei*, *Gou*, and *Sotsu* timelines, external forces manipulate Ooishi. During *Tataridamashi-hen*, he escorts a social worker to Satoko Hojo's residence following abuse rumors against her uncle, Teppei. Unbeknownst to Ooishi, Satoko stages the scene and injects him with H173, inducing Hinamizawa Syndrome. Accelerated paranoia leads him to frame Teppei for vandalism and spread curse fears. On the festival night, after Satoko murders Teppei and implicates Rika Furude, a terminal-stage Ooishi attacks villagers and club members with a gun and bat, killing Rika before Satoko executes him.

In *Nekodamashi-hen*, a deranged Ooishi assaults Rika at the festival, demanding answers about the curse and killing bystanders, including Mion and Shion Sonozaki, culminating in him beating Rika to death. Subsequent loops show him attempting to intervene in Akasaka's hostage crisis at Rika's shack. Post-retirement, his book with Akasaka reflects his unresolved obsession with the curse, framing his legacy as both a justice-seeker and an unwitting pawn in Hinamizawa's cycles of tragedy.