Rena Ryūgū, born Reina in Hinamizawa, relocated to Ibaraki during childhood following her mother’s career shift. Her family fractured after her mother’s affair and subsequent pregnancy, culminating in divorce and profound psychological wounds. Renouncing her given name, she excised the "i" to reject "icky things," a symbolic purge of painful memories. Trauma-fueled violence erupted in assaults on peers and property destruction, resulting in psychiatric hospitalization. There, delusions of maggots tainting her blood surfaced, interpreted as Oyashiro-sama’s curse, compelling her belief that only a return to Hinamizawa could grant absolution.

Back in Hinamizawa, she embraced a buoyant facade, fixated on hoarding "cute" treasures through compulsive "Take Home Mode" antics. This whimsy cloaked inner turmoil, epitomized by a clandestine junkyard sanctuary stocked with discarded relics she deemed forsaken. Fierce loyalty to her father spurred ruthless pragmatism, driving her to lethal self-defense against swindlers exploiting him—a stark testament to her duality as protector and aggressor.

Her conviction in Oyashiro-sama’s wrath and acute lie detection frequently ignited volatile confrontations. A clash with Keiichi exposed this fragility: accusations of hypocrisy escalated into a frenzied pursuit. Hinamizawa Syndrome—breeding paranoia and hallucinations—anchored her oscillation between gentleness and ferocity. Keen intuition, like discerning deceit through gaze or reconstructing crimes, pierced through her ditzy exterior, revealing latent shrewdness.

Later arcs cast her as a strategic force against corruption, intimidating village leaders to shield Satoko from abuse. Methodical planning replaced past impulsivity, showcasing growth. Even so, vulnerability lingered; during a school siege, Keiichi’s intervention quelled her rage, averting carnage and underscoring her potential for remorse.

Adult iterations portray her at university, sustaining bonds with Keiichi and Mion. A bloodied cap clings as a relic of unhealed scars. Alternate timelines, like "Rei," introduce a son, Kihiro, decades post-original events, cementing her enduring legacy within the community.

Her narrative weaves yearning for normalcy with scars from betrayal and supernatural dread. This interplay crafts a layered portrait of resilience—a soul straddling self-reinvention and the ghosts of trauma, eternally grappling with identity amid chaos.