Kazuya Ayanokōji, eldest scion of the Ayanokōji lineage, collaborated with his grandfather Reitarō in clandestine experiments to forge Absolute Angels—superhuman weapons of immense power. A decade before the central narrative, he recklessly awakened the primordial Absolute Angel Cielo against Reitarō’s warnings, triggering the cataclysmic Seven Days of Hot Snow. The disaster fractured Cielo into four entities: Murakumo, Batraz, Claíomh Solais, and the bisected Megingjord. Presumed dead afterward, Kazuya survived, his body altered by Cielo’s Mana into an inhuman vessel granting supernatural abilities.

Egomania and theatricality fuel his contempt for siblings, whom he deems beneath him, openly ridiculing their endeavors as futile while demanding their emulation. His cruelty manifests in calculated malice: he psychologically tortured his sister Mika by stealing her first love, later escalating to her murder and physical abuse of his brothers. Kazuya’s relationship with youngest sibling Kyoshiro hinges on deception—his apparent sacrifice to save Kyoshiro during the catastrophe was incidental, a byproduct of removing him as an obstruction.

Transformed by Cielo’s energy, Kazuya wields thorned vines erupting from his hands, teleportation, and Mana-draining kisses to siphon power from Absolute Angels. Obsessed with restoring Cielo’s original form, he dismisses global annihilation as collateral damage, kidnapping Angels like Kū, Cielo’s physical vessel, to fulfill his goal.

His downfall arrives when the Angels’ bonds with their partners fracture Cielo’s unity. Kū sacrifices herself to liberate the Angels, shattering Kazuya’s plans. Defeated, he is left wheelchair-bound and mentally broken, tended by Valteishia, Cielo’s soul fragment. His legacy lingers in familial scars, most profoundly affecting Kyoshiro, whose shattered idolization unveils Kazuya’s true nature as a manipulative destroyer.