Atsushi Nakajima, an orphan scarred by years of physical and psychological torment at a government facility, suffered under a director who masqueraded as a paternal figure while enforcing brutal punishments—from isolation and forced injections to hammering nails into his flesh. His expulsion at eighteen, falsely attributed to funding shortages, concealed the truth: uncontrollable transformations into a destructive white tiger under moonlight. His striking appearance features light gray hair slashed by a stark black streak and segmental heterochromia blending purple and yellow irises, paired with an asymmetrical haircut—a lingering mark of childhood cruelty. Upon joining a detective agency, he dons an outfit stitched together by colleagues, complete with a belt that sways like an emotive tail. Tormented by self-doubt yet driven to prove his worth, he wrestles with deeply ingrained feelings of inadequacy. His instinctive heroism surfaces in acts like rescuing a suicidal stranger or shielding bystanders from a bomb during his agency initiation. A steadfast moral compass leads him to protect even adversaries, steering figures like Kyōka Izumi and Lucy Maud Montgomery from violence through empathy. His ability, *Beast Beneath the Moonlight*, unleashes a regenerative white tiger. Once a chaotic force, he masters partial and full transformations through the agency’s guidance. Collaborative battles with Ryūnosuke Akutagawa sharpen his combat strategy, though high-stakes conflicts still demand reliance on allies. Key relationships—mentorship from Osamu Dazai, a volatile partnership with Akutagawa, and protective ties to Kyōka and Sigma—slowly mend his fractured psyche, though trauma resurfaces in nightmares and guilt. His growth emerges during clashes with the Port Mafia, the Guild, and the Decay of the Angel, confronting global crises while grappling with his past. The orphanage director’s death ignites turbulent grief, exposing unresolved loyalties. Flashbacks and dialogues trace his struggle toward self-forgiveness, marked by decisive leadership in critical missions. His narrative echoes *Sangetsuki*—the tale of a man-tiger’s identity crisis by his literary namesake. Across his journey, resilience intertwines with compassion amid abuse’s shadow. Steady gains in confidence and purpose, fueled by alliances and an unwavering vow to protect others, chart his path from fractured orphan to guarded hero.