Chuuya Nakahara originated within a military facility as the vessel for Arahabaki, an entity embodying calamity and destruction. Around age seven, Arthur Rimbaud's infiltration triggered Arahabaki's release, forming Suribachi City and erasing Chuuya's earlier memories. Freed by an unknown party, he joined the Sheep—a youth self-defense group—becoming their protector through gravity manipulation. Though not their official leader, his role as their "trump card" earned him the title "King of the Sheep." At fifteen, a Port Mafia attack on the Sheep drove Chuuya to investigate his connection to Arahabaki. This led to clashes with Osamu Dazai and Ryūrō Hirotsu. Port Mafia boss Ōgai Mori coerced Chuuya's cooperation by taking Sheep hostages, forcing him to partner with Dazai. Together, they exposed the truth: Rimbaud had accidentally released Arahabaki while attempting its theft, with Chuuya acting as its living seal. After defeating Rimbaud, Chuuya received a hat as a gift upon joining the Port Mafia, symbolizing his entry. Dazai manipulated the Sheep into believing Chuuya betrayed them, prompting an alliance with the GSS that resulted in Chuuya being stabbed. Surviving, he was formally recruited by Mori, who withheld documents about Chuuya’s origins—possibly identifying him as an artificial clone or modified human—as leverage. At sixteen, assassination attempts by Paul Verlaine (Rimbaud’s former partner) deepened Chuuya’s Port Mafia ties and his partnership with Dazai, now called "Double Black." Chuuya exhibits a volatile temper, pride in combat prowess, and blunt arrogance. He relishes challenging fights but disengages pragmatically when negotiation serves the Port Mafia. Though ruthless against threats, he avoids gratuitous brutality, condemning Dazai’s corpse desecration. His unwavering loyalty shifted from the Sheep to the Port Mafia, where he rose to executive rank. He fiercely values subordinates and despises betrayal, demanding Q’s execution for killing his men. His existential struggle stems from missing pre-age-seven memories and an inability to dream. Long doubting his humanity due to Arahabaki, he adopted restraint: favoring kicks over punches and reserving barehanded combat for mortal threats. Rimbaud’s dying plea—to "live as a human"—partially eased this crisis, though Mori’s revelations left his identity ambiguous. His defining trait is a vitriolic rivalry with Dazai, whom he instantly disliked for manipulative tactics. Dazai exploited this, provoking Chuuya’s temper to control him and engineering the Sheep’s betrayal. Despite this, Chuuya acknowledges Dazai’s strategic genius and cooperates in dire scenarios, notably during "Corruption." His ability, "For the Tainted Sorrow," controls gravity and gravitons, enabling flight, environmental manipulation, and projectile deflection. Its true form, "Corruption," unleashes Arahabaki’s full power: increasing density to crush tanks and generating pseudo-black holes. Activation requires the chant: "Oh, Grantors of Dark Disgrace, Do Not Wake Me Again." Corruption erodes sanity and causes lethal bleeding unless nullified by Dazai’s ability. Removing gloves signals its use, honoring his restraint philosophy. Post-Port Mafia recruitment, Chuuya adopted orange hair, a chained black hat, a black choker, and a cape-style long coat over a gray vest and cropped jacket, always wearing gloves. During his Sheep tenure, he wore a gray pea coat and a ram-emblazoned blue bracelet. Later, he staged a vampire transformation with red contacts and false fangs to infiltrate a plot by Fyodor Dostoyevsky, a mission alongside Dazai underscoring their volatile partnership.