Hone-Onna began as Tsuyu, a geisha renowned for crafting paper balloons. Betrayed by her lover Shinsaburo, who sold her to a brothel to erase his debts, she bonded with fellow prostitute Kiyo and met Tetsuya, a man who offered genuine affection. Tsuyu orchestrated Kiyo’s escape with Tetsuya, sacrificing her own chance at freedom. Kiyo, seized by jealousy, exposed their plan to the brothel owner, leading to Tsuyu and Tetsuya’s murder. Tsuyu’s body was cast into a river, merging with the bones and spirits of other murdered women to birth the yōkai Hone-Onna. Newly formed, Hone-Onna wandered villages seeking companionship. Yet her uncontrolled skeletal visage terrified humans, deepening her solitude. Ai Enma approached her, offering partnership. Hesitant but sensing kinship, Hone-Onna became Ai’s third assistant—the first among them to have once been human. Serving Ai, Hone-Onna investigates clients and targets under the alias "Sone Anna." She typically appears as her human self—an elegant woman in traditional attire like a blue kimono with a front-tied red obi, reflecting her past. Seasonal shifts alter her kimono colors and accessories; undercover missions see her in modern clothes, hair loose or ponytailed. Mild-mannered and empathetic, she shows more overt concern than Ai’s other companions. She resents being called "obaasan," a taunt Kiyuri employs. Her powers include traversing realms, instantaneous attire shifts, memory-based illusions, and transforming into a red straw doll by looping her obi-jime around her neck. She reveals her skeletal form to instill terror, wields knife-like objects wreathed in blue spirit fire, and contorts to infiltrate tight spaces—though extraction challenges her. After Ai’s demise in "Three Vessels," Hone-Onna tended a bar until Ai’s spirit—manifested as a butterfly—recruited her anew. She later posed as a gym teacher at Yuzuki Mikage’s school for investigations. When Yuzuki briefly assumed the Hell Girl mantle, Hone-Onna and Ren Ichimoku withheld aid, suspecting Tsugumi Shibata’s departure stemmed from her failure to change Yuzuki’s fate. Upon Ai’s return as Hell Girl, Hone-Onna resumed her role.