Born Reina Ryūgū in Hinamizawa, Rena relocated to Ibaraki with her family as a child. Her parents' divorce, precipitated by her mother's affair and pregnancy, inflicted deep trauma. Blaming herself, Rena suffered a mental breakdown, assaulting three male classmates with a baseball bat and shattering school windows. Hospitalized, she developed delusions of maggots infesting her blood and attempted self-harm. She claimed Oyashiro-sama commanded her return to Hinamizawa for safety, symptoms later identified as Hinamizawa Syndrome, a condition resembling schizophrenia and delusional parasitosis. Returning to Hinamizawa around April, she adopted the name Rena, omitting the "i" from "Reina" to symbolize shedding "icky" elements of her past. She integrated into the local school and joined the after-school games club. Rena projects a cheerful, friendly demeanor, often entering "Cute Mode" upon encountering objects or people she finds adorable, exclaiming "Hauu~! Omochikaerii~!" ("I want to take it home!"). This state heightens her physical abilities, granting unusual agility and persistence. Her speech features verbal tics like repeating "kana, kana?" ("I wonder?"). Despite her kind exterior, Rena reacts with violence to deception or challenges to her belief in Oyashiro-sama. She harbors an intense aversion to lies, marked by the outburst "Uso da!" ("That's a lie!"). Keenly perceptive, she deduces complex situations from minor details, such as pinpointing a character's location through household clues. Her junkyard "treasure hunts" function as both hobby and emotional refuge; she maintains a secret base in an abandoned van filled with collected items. Rena fiercely protects her father. In Tsumihoroboshi-hen, she killed scam artists Rina Mamiya and Teppei Hōjō to shield him from exploitation, methodically disposing of their bodies. After acquiring Takano Miyo's scrapbook, distrust led her to take schoolchildren hostage, planning mass murder-suicide. Keiichi Maebara intervened, averting tragedy. Rena later expressed remorse for this incident. Mature in later arcs, Rena witnessed the formal end of Oyashiro-sama's curse. By 1988, she enrolled at Gogura University alongside Keiichi and Mion Sonozaki. By 2019, she had a son named Kihiro, referenced in Higurashi no Naku Koro ni Rei. Physically, Rena has short orange hair cut asymmetrically with spiky bangs and light blue eyes. She stands 161 cm tall, typically wearing a sailor-style school uniform with a yellow necktie. Her casual outfit includes a white dress with purple bows, black thigh-high socks, brown knee-high boots, and a white beret. During intense emotional shifts, her eyes appear to lose visible light, creating an unsettling effect. Rena holds unspoken romantic feelings for Keiichi, acknowledging Mion Sonozaki's interest without altering her behavior. She frequently targets Rika Furude and Satoko Hōjō during "Cute Mode" due to their punishment outfits. Her loyalty to friends contrasts her capacity for brutality when betrayed, evident when she attacked Mion during the school hostage crisis.