Yūhi Amamiya, a college student burdened by apathy and cynicism, carries scars from a childhood fractured by betrayal. After his father’s death and mother’s disappearance, his grandfather imprisoned him in a basement, weaving psychological chains to sever all human connection. This abuse forged a reclusive young man who views the world through a lens of distrust, clinging to solitude as both armor and refuge.

Slender and unremarkable at first glance, Yūhi’s green eyes and disheveled black hair frame a face often blanketed in indifference, though flickers of mischief surface in rare moments of levity. His habitual hoodies and jeans mirror a desire to vanish into the background. Yet beneath this frailty lies a razor-sharp mind. Confronted by supernatural dangers, he devises cunning strategies to offset physical limitations, wielding an innate power: Domain Control. Initially permitting only fleeting levitation to evade threats, this ability blossoms into Airspace Control: Babylon—a technique that warps velocity, accelerating his movements while ensnaring adversaries in slowed time.

His life pivots when Asahina Samidare, a princess bent on annihilation, offers him purpose. Swearing loyalty, Yūhi replaces his grandfather’s shackles with voluntary servitude to her cause. Their bond, born of mutual skepticism, deepens into an alliance where survival intertwines with fragile affection. Driven by devotion to Samidare’s apocalyptic ambition, he sheds passivity, engaging in battles that test his resolve.

Tutored by Shinonome Hangetsu, Yūhi adapts martial arts to his fragile physique, mastering techniques like Houtengeki despite initial struggles. His growth eclipses even Hangetsu’s legacy, culminating in victories over rivals such as Mikazuki, Hangetsu’s brother. In combat, Yūhi thrives on deception, concealing his true strength to exploit opponents’ arrogance.

Though prone to crass humor and invasive antics, Yūhi’s icy exterior thaws through alliances with fellow Beast Knights. A bitter rivalry with Mikazuki evolves into grudging respect, their clashes reflecting divergent worldviews. Brief vulnerabilities—grieving Hangetsu’s death, hesitating mid-duel—hint at buried empathy.

Samidare’s crusade to dismantle the world initially aligns with his nihilism, but exposure to the knights’ sacrifices sparks conflict. Witnessing their resilience, he grapples with nascent morality, ultimately embracing a hero’s role against cataclysmic threats. His final acts defy destruction, prioritizing preservation through evolved Domain Control and tactical ingenuity.

A contractual wish to heal his tormentor-grandfather lingers as a ghost of old loyalties, yet Yūhi’s journey charts a broader metamorphosis: from isolated survivor to connected guardian, his redemption anchored in the fragile trust he once scorned.