Kyoka Izumi begins as a young assassin for the Port Mafia before finding refuge with the Armed Detective Agency. She possesses dark blue or black hair, often in low twin-tails adorned with flower pins, and blue eyes that shifted from dull to clearer after leaving the Mafia, reflecting her emotional evolution. Her signature attire includes a red kimono with sprout-like patterns, a yellow datejime belt, long white socks, sandals, and yellow and red wrist pads. She constantly carries a tiny rabbit doll and wears a cellphone on a necklace, the latter initially vital for activating her ability. Her childhood was happy until assassins killed her parents. Her father, a former government agent turned freelancer, was manipulated by an ability user to attack her. Her mother, wielder of the supernatural ability Demon Snow, killed him to protect Kyoka but was then controlled herself. With her final act, Kyoka's mother imperfectly transferred Demon Snow to Kyoka, linking its control to the cellphone she had recently gifted her daughter. Orphaned, Kyoka was taken in by the Port Mafia and trained under Kouyou Ozaki as a protégée. During her Mafia tenure, Kyoka earned the moniker "Thirty-Five Count Murderess" for killing 35 people in six months. This period shaped her into an emotionless, detached, and ruthlessly obedient figure, resembling a doll. She believed her sole purpose was killing and felt deserving of death. Her encounter with Ryunosuke Akutagawa, whom she begged to destroy Demon Snow and kill her, solidified this worldview. Her transformation started when assigned to bomb a train with Motojiro Kajii. Confronted by Atsushi Nakajima, she followed Akutagawa's order to protect the bomb, dispassionately revealing her identity and body count. When the bomb's timer unexpectedly shortened, Kyoka rejected the Port Mafia's influence, declared she no longer wished to kill, and attempted to sacrifice herself by jumping with the bomb. Atsushi saved her, tearing off the bomb and shielding her from the blast, marking her first step toward redemption. Recovering at the Armed Detective Agency, Atsushi introduced her to simple joys like tofu and crepes, rekindling her childlike curiosity. Though planning to surrender to authorities, Akutagawa intervened, leading to a confrontation where Kyoka again sought self-sacrifice. Atsushi rescued her once more, and she formally requested to join the Agency, vowing to prove she was more than a killer. Agency President Yukichi Fukuzawa accepted her, and Osamu Dazai arranged for her to share a dorm with Atsushi for protection. Her ability, Demon Snow, materializes a sword-wielding phantom. Initially, it obeyed only orders sent via her cellphone due to the imperfect transfer. After joining the Agency, Fukuzawa's ability allowed Kyoka to control Demon Snow directly. Later revelations confirmed Demon Snow embodied her mother's protection, not the cause of her parents' deaths. During the Guild arc, Kyoka faced Kouyou, who tried to reclaim her for the Mafia. Kyoka feigned compliance but attacked Kouyou, affirming her loyalty to the Agency. When Guild leader Francis Fitzgerald captured Atsushi, military police arrested Kyoka. Confined in a drone, she initially resigned to death until Dazai convinced her to act. She collided the drone with the Guild's airship Moby Dick to save Yokohama, an act Fukuzawa deemed her official entrance exam. His ability freed her, and Demon Snow aided her escape. The Agency celebrated her as a full member. Post-Guild, Kyoka struggled to trust Demon Snow until she and Atsushi discovered documents exonerating it from her parents' deaths, enabling reconciliation. She retains skills from her past: infiltration, lockpicking, swordplay, acrobatics, anatomy knowledge, exceptional memory (memorizing maps, wanted lists, city layouts), driving expertise, and hinted acupuncture knowledge. Her personality evolved from emotionless obedience to a blend of adolescent curiosity and stoic resolve. She enjoys rabbits, tofu, hydrangeas, and ghosts, while disliking dogs, thunder, and flies. She maintains a shaky moral code, willing to harm others non-lethally to protect the Agency or innocents. She shares a close, protective bond with Atsushi, viewing him as her savior and light. Her journey centers on atoning for past crimes while embracing a new identity as a detective.