Rion, sole daughter of the Beast King of the East, Kirinmaru, and niece of the enigmatic Zero, spent her early years shadowing her father in his global conquests. During a pivotal clash six centuries before the central narrative, she stood witness to his defeat by Tōga, the Beast King of the West, whose rebuke for involving a child in warfare left an indelible mark on her psyche, cementing her disdain for bloodshed. When Kirinmaru’s rampage against a rival kingdom escalated, Rion became a pawn in the conflict—captured and slain by the vengeful half-demon Sakasa. Desperate to preserve her, Kirinmaru tethered her spirit to a clay doll crafted from her bones and grave soil, imprisoning her essence within Mount Musubi to bar her soul’s passage to the afterlife. Centuries passed as she lingered in limbo, her whispers to her father carried only by the fragile Dream Butterflies until her eventual resurgence.

Reborn within a synthetic humanoid vessel mirroring her original form—crimson-short hair, fawn-like ears, and pale azure eyes—Rion allied with the Half-Demon Princesses Towa, Setsuna, and Moroha. She armed them with the Kyūyōkon Root and bestowed Towa the Star-Slicer Flute, a relic that morphed into the demonic blade Zanseiken. This sword, paired with Kirinmaru’s Bakuseiken, proved vital in thwarting the Demon Spirit Beast. Driven by dread of her father’s manipulation of the Windmill of Time—a act she believed would herald the catastrophic Degenerate Age—Rion sought to dismantle his ambitions to protect the world she loved.

Her resolve led her to confront Kirinmaru’s proxies: Riku, born from his severed horn, and Osamu Kirin, whose deception tricked her into fusing with the Grim Butterfly. The merger twisted her spirit, stoking bitterness toward her father’s destructive obsessions and his perceived selfishness. Freed when the Princesses severed the Grim Butterfly’s bonds, Rion reclaimed her innate compassion, reconciling her lingering love for Kirinmaru. In their final encounter, she embraced him, yearning for peace as their souls departed the mortal realm together.

Rion’s arc traces her evolution from a captive spirit to a conflicted ally, a briefly corrupted adversary, and ultimately a figure of redemption. Her journey navigated the tension between filial devotion and the greater good, shaped by pivotal bonds: her alliance with the tormented Riku, who defied Kirinmaru to aid her, and her fraught kinship with Zero, whose choices illuminated the burdens of legacy and sacrifice.