Kyōka Izumi is a teenage girl introduced as a Port Mafia assassin who later joins the Armed Detective Agency. She possesses short stature, dark hair worn in low twin-tails secured with flower pins, and blue eyes that shift from dull to clearer after leaving the Mafia. Her standard outfit is a red kimono featuring sprout patterns, paired with a yellow datejime belt, white socks, sandals, and yellow-red wrist pads. She carries a rabbit doll and a cell phone on a necklace, the phone initially essential for controlling her ability. Alternative attire includes a maid uniform, disguise clothing, a white gown worn during military captivity, and tactical gear after the Agency is framed. Her parents, both assassins, died during a home invasion orchestrated by enemies who manipulated her father using a blood-based ability, forcing him to attack her. To protect Kyōka, her mother transferred the ability Demon Snow to her, imperfectly linking it to her cell phone rather than her will. This flaw caused Kyōka to mistakenly believe her own ability caused her parents' deaths. The Port Mafia subsequently recruited her. Trained by Kōyō Ozaki, she became a ruthless operative nicknamed the "Thirty-Five Count Murderess" for killing thirty-five people within six months. During this period, she exhibited emotional detachment, executing orders without hesitation or remorse in a doll-like state. A mission involving a train bombing marked a turning point. Ordered to kill Atsushi Nakajima and detonate a bomb, she instead expressed a desire to stop killing and attempted suicide by jumping with the bomb. Atsushi rescued her, destroying the bomb and sparing her life, initiating her departure from the Port Mafia. She initially surrendered to authorities, accepting potential execution, before the Armed Detective Agency intervened. Under Yukichi Fukuzawa’s guidance, she gained full control over Demon Snow, eliminating the need for the phone. After joining the Agency, Kyōka adopted a more typical teenage demeanor, showing curiosity about everyday experiences like crepes, arcades, and city exploration. She keeps a rabbit plushie gifted by Atsushi and developed a large appetite, particularly for tofu and sweets. Her moral compass remains pragmatic; while vowing to avoid killing, she will harm enemies to protect the Agency and is capable of vengeful actions, such as threatening Ryūnosuke Akutagawa. She fears thunder and dislikes isolated spaces like bathrooms due to vulnerability to ambushes. Her skills encompass swordsmanship, acrobatics, infiltration (lockpicking, disabling security), memorization (e.g., maps, target lists), driving, anatomy knowledge, and cooking. Her ability, Demon Snow, manifests a sword-wielding phantom guardian capable of high-speed strikes and immense force. Her relationship with Atsushi is central; she views him as a source of safety, shares living quarters with him, and prioritizes his well-being. She demonstrates fierce loyalty to the Agency, willing to sacrifice herself to save Yokohama during the Guild conflict. Her development involves overcoming self-hatred for past crimes and finding purpose in protecting others. She references this growth, stating she belongs with the Agency and fights to prove she is more than a weapon.