Akiko Yosano is the physician for the Armed Detective Agency, wielding a unique healing ability called "Thou Shalt Not Die." This power activates only when the recipient is near death or critically injured, manifesting as golden butterflies that emerge from her body and heal wounds upon contact. Because minor injuries don't trigger it, she must inflict severe harm before healing, earning her a reputation among colleagues for sadistic methods and causing them to actively avoid her care. Her ability draws inspiration from the real-life poet Akiko Yosano's anti-war poem of the same name, embodying themes of life preservation. She stands at 166 cm tall, weighs 52 kg, and has blood type O. Her appearance features straight dark hair cut in a chin-length bob with bangs and striking magenta eyes. A distinctive golden butterfly hairpin, gifted by a soldier named Shunzen Tachihara during her time as a wartime medic, adorns the left side of her head, symbolizing a rare moment of gratitude amidst trauma. Her typical attire includes a white button-up blouse with puffy sleeves, a black tie, a knee-length black skirt, black tights, medical gloves, and red heels. For missions or specific events, she wears varied outfits like military aprons, prison uniforms, or riot gear. Yosano's personality blends grace with assertiveness, reflecting strong feminist ideals and a disdain for male chauvinism. She holds human life sacred, reacting violently to those who trivialize death, such as Port Mafia member Motojirō Kajii. This contrasts with her morbid interests: reading obituaries and collecting crime-scene corpse photos, which she views as impartial records of human equality in death. She enjoys shopping, Japanese sweets (wagashi), eels, sake, and flowers, often socializing over drinks. Despite her usual composure, she exhibits fierce aggression when provoked, wielding weapons like cleavers or chainsaws in combat or during healing sessions. Her background centers on childhood trauma during the Great War. Recruited at age 11 by Ōgai Mori for the 356th Division Infantry Corps, her ability forcibly revived soldiers repeatedly. This cycle, intended to demonstrate supernatural advantages to officials, caused psychological breakdowns among troops, culminating in Shunzen Tachihara's suicide after multiple near-death experiences. The trauma led Yosano to sabotage her military ship, resulting in postwar isolation until Mori attempted to reconsign her three years later. Yukichi Fukuzawa and Ranpo Edogawa intervened, rescuing her by inviting her into the Armed Detective Agency and rejecting Mori's exploitation. Ranpo's emphasis on valuing her kindness over her ability proved pivotal for her emotional recovery. Beyond her supernatural power, Yosano possesses extensive medical knowledge, including physiology and anatomy, enabling precise injury assessment. She demonstrates combat proficiency, often engaging in close-quarters fights to incapacitate foes for healing. Her leadership emerges during crises, such as coordinating escape plans when the Agency is targeted by Hunting Dogs.