Akiko Yosano is the physician of the Armed Detective Agency, a young woman with a refined appearance marked by straight black hair cut in a bob with bangs, magenta eyes, and a pale complexion. She typically wears a white blouse with puffy sleeves, a black tie, a black knee-length skirt, black tights, and red high heels. A golden butterfly-shaped hairpin is always fastened on the left side of her head. Yosano carries herself with grace and dignity, identifying as a feminist who rejects sexist behavior and believes in equal rights. Beneath her composed exterior, she has pronounced sadistic tendencies, especially when performing her medical duties. Her extraordinary healing ability is called Thou Shalt Not Die, which can instantly regenerate any external wound, reattach lost limbs, and heal near-fatal injuries. However, the ability only activates when the patient is on the brink of death; for minor wounds, she must first inflict life-threatening damage, often using a cleaver, axe, or chainsaw. This process she approaches with unsettling enthusiasm, causing even her allies to fear her treatment. Yosano places an extremely high value on human life and becomes fiercely angry when others treat death carelessly. This conviction stems from her traumatic past. At age eleven, during the Great War, she was forcibly conscripted by the military physician Ogai Mori while working at a confectionery store. He used her ability to create an immortal regiment, forcing her to repeatedly heal the same soldiers so they could be sent back to the front lines. A soldier she saved gave her the golden butterfly hairpin and called her an angel, but the endless cycle of death and resurrection drove him to suicide, and he called her the Angel of Death. Overcome with despair, Yosano sabotaged her ship and was imprisoned, then held in isolation after the war. Three years later, she was rescued by Yukichi Fukuzawa and Ranpo Edogawa, who invited her to join the newly formed Armed Detective Agency. Ranpo assured her that they valued her kindness, not just her ability. Within the agency, she mentors younger members and remains deeply resentful of Mori, now the Port Mafia boss. Despite her violent methods, Yosano is a skilled physician and a loyal protector of life, using her power to ensure that no one else endures the meaningless suffering she witnessed as a child.