Kōyō Ozaki holds an executive position within the Port Mafia, signifying her considerable power and combat skill. A formative trauma shaped her past: a failed escape attempt alongside an admired man resulted in his execution by the former Port Mafia leader. Though the precise reason for her survival remains unclear, her valuable ability and potential for rehabilitation may have been factors. This event cemented her cynicism towards hope and love, convincing her that those born in darkness, like herself, cannot survive in the light without destruction. She harbored lasting resentment toward the former boss, though not his successor, Ōgai Mori, under whom she rose to executive rank. Early in Mori's leadership, she supervised Chūya Nakahara's integration into the mafia, leading him to call her "ane-san" (elder sister), an address she eventually accepted. Physically, Kōyō possesses a tall, slender build. Her hair, depicted as light scarlet or pink depending on adaptation, is styled in a traditional Japanese bun secured by golden kanzashi hairpins (three in manga, often two in anime) and an additional clip featuring a light pink furry element and red ribbon forming a five-petal flower. Her eye color varies between violet (manga) and cherry red (anime). She wears red eyeshadow, light pink lipstick, and red nail polish. Her attire consists of a black-and-pink kimono adorned with red spider lily patterns, tied with a maroon obi featuring bellflower or maze-like designs (varying by adaptation), and covered by a mantle that gradients from light pink to darker shades toward the bottom, sometimes embellished with flowers. She completes her look with brown lace shoe heels and often carries a red Japanese umbrella concealing a sword. Her personality blends grace and composure with deep-seated ruthlessness rooted in her past. She embodies a jaded worldview, frequently stating her belief that individuals rooted in darkness, especially assassins like herself or her protégée Kyōka Izumi, cannot survive in the light without being consumed. She expresses this philosophy through floral metaphors, viewing people as flowers destined to bloom in darkness or wilt in light. Despite her cynicism, she enjoys camaraderie and leisure with fellow executives like Mori and Hirotsu. However, she exhibits intense protectiveness, possessiveness, and warped concern for Kyōka Izumi, whom she mentored. This manifested in psychologically manipulative tactics, including instilling a fear of change and falsely blaming Kyōka for her parents' deaths, aiming to bind her to the Port Mafia. This attachment drove her to attack a Special Division for Unusual Powers transport to reveal Kyōka's past and later refuse to harm Kyōka physically. While capable of typical mafia cruelty and violence, including exploiting battle openings and verbal aggression, Osamu Dazai's intervention shifted her perspective; he persuaded her to relinquish obsessive control over Kyōka. Following this, she showed reluctant concern for Kyōka's well-being and even her associates, expressing disinterest in harming Kyōka's friends. She also displayed pragmatic fear, particularly regarding enduring Dazai's torture methods. Her combat ability, Golden Demon (金色夜叉, Konjiki Yasha), materializes and controls a large, sword-wielding phantom guardian possessing significant strength and speed. She directs this entity with her own will, distinguishing her control from Kyōka Izumi's similar power. This ability, directly referencing Ozaki Kōyō's novel *The Golden Demon* and its themes of humanity lost to greed, is tailored for lethal combat with limited non-lethal applications, reinforcing her belief in destinies within the mafia. She has wielded it effectively in battles, such as against Jun'ichirō Tanizaki and Kyōka Izumi. Key relationships define her narrative. Her mentorship of Kyōka Izumi evolved into a complex, maternal-like bond marked by manipulation yet genuine, albeit toxic, care and protectiveness. She held a specific grudge against the former Port Mafia leader for executing her escape partner, yet serves loyally under Ōgai Mori, even addressing him by his first name. She supervised Chūya Nakahara upon his mafia entry, fostering a relationship where he calls her "ane-san." Her interactions with other mafia members vary, showing distrust and passive-aggression toward figures like Ace while maintaining respect among peers. Her dynamic with Dazai is notable, as his intervention forced her to confront her actions toward Kyōka, and she exhibits clear apprehension toward his methods. Personal preferences include liking kinpura (sweet potato and chestnut simmer) and pickles, and disliking hope, love, and Atsushi Nakajima, whom she blamed for Kyōka's defection. She shares a birthday, January 10, with Yukichi Fukuzawa.