Kunihiko Yamada, known as Yamabiko, begins life as a human middle school student with dark brown hair, brown eyes, and a cruel disposition—traits later contradicted by ambiguous records of his appearance. His fate alters when Kodama, a reality-warping figure, extends unexpected kindness to him. Amid a devastating tumor-plagued epidemic, he consumes her blood in a desperate attempt to assist her, triggering an irreversible metamorphosis into a towering, sleek black canine with a lush tail and unnervingly human eyes.

Cursed with immortality, he spends 5,000 years adrift through fractured dimensions, stripped of emotion or direction, until rediscovering Kodama in the Festival Forest. There, he vows eternal loyalty, embracing his role as her guardian. Unbeknownst to him, his latent power to manifest thoughts had subtly warped Kodama’s reality, exacerbating the plague’s devastation. Tormented by guilt over his failure to challenge her choices during the crisis, he vacillates between blunt criticism and silent awe for her resilience—a tension amplified by War, whose Scar Art ability ignited the epidemic.

Millennia later, he guides displaced students through an alternate realm, unraveling truths of their malleable reality and its deity-like principal. His canine form stands as both a testament to unwavering devotion and a self-inflicted punishment for his human-era ruthlessness. Though he masks his emotions, flickers of remorse surface when confronting his past and Kodama’s unyielding resolve—a fragile counterpoint to his otherwise detached existence.