Kyūketsuki, a high-ranking vampire oni, wields blood both as sustenance and a weapon, channeling it lethally through his concealed fangs—the core of his power. Masking these traits, he infiltrates human society, his true nature emerging only when primal instincts override restraint. His name, meaning "vampire" in Japanese, mirrors this duality of predator and hidden identity.

Tragedy defines his past: across different narratives, he either kills his human bride during their wedding or awakens to her lifeless body, her death unresolved. Both versions anchor his torment in the clash between oni savagery and fleeting human connection, fueling self-loathing.

Temporarily allying with Carrot, a former oni, Kyūketsuki orchestrates a town’s massacre but singles out Sally as a priority threat. In combat, he exploits blood to immobilize foes by hardening their garments, yet Sally’s immunity to oni powers disrupts his tactics. Despite formidable prowess, he meets his end when Frau, a rabbit demihuman reclaiming her latent strength, strikes a fatal blow.

Dying, Kyūketsuki confronts his irreconcilable nature—oni instincts warring with human emotion—with bitter acceptance. His final words hint at daylight vulnerability, a fleeting nod to vampiric lore. Through his struggles and alliances, the narrative interrogates identity, prejudice, and violence’s cyclical grip, framing him as both perpetrator and casualty of societal rejection.