Hone-Onna, originally a geisha named Tsuyu skilled in crafting paper balloons, suffered betrayal when a man named Shinsaburo sold her to a brothel despite professing love, using the money to settle his debts. In the brothel, she befriended a prostitute named Kiyo and garnered genuine affection from a man named Tetsuya. Tsuyu engineered an escape for Kiyo and Tetsuya, prioritizing Kiyo's freedom. Kiyo, however, betrayed them to the brothel owner out of jealousy, leading to the murder of Tsuyu and Tetsuya by the owner's enforcer. Tsuyu's discarded body merged with the bones and spirits of similarly murdered women in a river, transforming her into the yōkai Hone-Onna, meaning "Bone Woman".

Following her transformation, Hone-Onna wandered near villages seeking companionship, but her inability to control her skeletal form caused people to flee in terror upon discovery, deepening her sorrow. Ai Enma located her and offered her service. Hesitant at first, Hone-Onna ultimately accepted after sensing something compelling about Ai, becoming the third companion and the first among them to have once been human.

As Ai Enma's assistant, Hone-Onna investigates targets for damnation, often infiltrating human society using disguises. For this work, she adopts the alias "Sone Anna," as her true name is unsuitable. Her standard appearance features a traditional kimono: blue with a dark blue border and red obi tied unusually in the front during earlier periods, later changing to white with dark blue accents in one season, and then to blue with yellow and red borders and a magenta obi. She accessorizes her hair with clips, cloth pieces, and hairpins, and wears red lipstick. For undercover work, she frequently wears modern attire like a light brown jacket over a gray top and black skirt, or a magenta jacket and skirt, often with her hair down or in a ponytail. When fulfilling a contract, she transforms into a dark red straw doll with a red string around its neck, typically preceded by tossing her obi-jime over her shoulder.

Her abilities include traveling between the human world and the Realm of Eternal Twilight, magically altering her attire, manipulating memories to create familiarity illusions, and partially or fully revealing her skeletal form to intimidate targets. She can pierce human flesh with her bone fingers. Though demonstrated only once, she possesses skill in throwing knives imbued with blue spirit fire and exhibits contortionist abilities allowing entry into tight spaces, though exiting proves more difficult.

Personality-wise, Hone-Onna generally maintains a mild, reserved manner. She exhibits concern and sympathy for human suffering more frequently than Ai's other companions. She reacts with annoyance, particularly to being called "obaasan" (old lady/auntie), a provocation often used by Kikuri, another entity associated with Ai, whom Hone-Onna frequently dislikes. Despite this friction, she demonstrates loyalty to Ai and the core group.

Following Ai Enma's death, Hone-Onna lived temporarily as a bartender until Ai's spirit, appearing as a butterfly, signaled her return. Subsequently recruited again, likely by Kikuri or Yamawaro, she assumed the role of a gym teacher at Yuzuki Mikage's school in Saigawara City while continuing her duties. Later, when Yuzuki temporarily assumed the role of Hell Girl, Hone-Onna and Ichimokuren refused to assist her. Instead, they sought out Tsugumi Shibata, suspecting her departure from Saigawara City was linked to her original intent to alter Yuzuki's fate, which had failed. After Ai Enma resumed her position as Hell Girl, Hone-Onna resumed her duties as Ai's companion.