Aki Myojin holds the position of Chief Security Guard at Black Wing Prison, a maximum-security facility. He possesses a tall, lean physique with defined musculature, sharp facial features, pale skin, and dark purple hair. His eye color shifts between gold in manga renditions and purple in anime adaptations. A prominent scar remains hidden beneath his attire. His standard uniform includes a black guard outfit with silver rank insignia, a hat, white gloves, and a whip. Off-duty, he dons a simple black suit and tie. Flashbacks reveal him with dyed blonde hair in his youth. Personality displays stark duality: exuding confidence and authority professionally, he shows warmth toward colleagues and most inmates, earning their trust. Yet toward inmate Hina Saotome, his demeanor shifts to publicly stoic and privately sadistic, particularly during sexualized punishments where he openly relishes her torment and humiliation—though Hina occasionally detects pity in his gaze. Underlying this cruelty is emotional anguish rooted in past trauma, including his mother’s critical illness. He self-reflectively brands his anger as "foolish," acknowledging his harmful actions. His possessiveness over Hina escalates violently when she interacts with fellow inmate Higa Yamato. Backstory reveals turmoil: strained youth with his mother during President Yuzuru Akatsuki’s courtship of her culminated in him telling her, "all you have to do is die." He later discovered her and Akatsuki hanged after death threats; he rushed her to Sanyou Hospital, where she remains comatose. Learning of Hina Saotome’s conviction for embezzling Akatsuki’s funds—which she denied—he responded with a dark smile, signaling personal stakes in her case. Upon Hina’s incarceration, he asserted dominance by assigning her number 3077, enforcing invasive body checks, and orchestrating punishments: locking her with dangerous inmates (foiled by Higa’s intervention), sabotaging her visit with boyfriend Yakumo, and raping her in a shower after an escape attempt. He extended her sentence, isolated her, revoked visitation rights, and transferred her to laundry duty. Exploiting psychological triggers, he bound her hands and raped her through prison bars while mocking her arousal. Obsession intensified: spotting Higa’s love bite on Hina, he inflicted prolonged punishment. He intercepted their interactions, molesting Hina before Higa to assert control. When Higa broke into his office seeking evidence of Hina’s innocence, Myojin whipped him but revealed inner conflict. Transferring both to a psychiatric wing, he raped Hina—restrained and blindfolded—as a "farewell gift" during transport, provoking Higa’s rage before a crash where Myojin shielded Hina, losing consciousness. Captured post-crash by Higa’s allies and hog-tied, he remained defiant. When Hina visited, he triggered her conditioned obedience via her prison number, compelling sex and demanding release—confirming her psychological enslavement beyond prison walls. He declared all others her enemies, cementing her status as his captive.