Hone Onna, also known as Bone Woman, is a supernatural entity and one of the primary companions assisting in the execution of vengeful contracts. Originally a human named Tsuyu, she was a geisha skilled in making paper balloons. She fell in love with a man named Shinsaburo, who betrayed her by selling her to a brothel to settle his debts. During her time there, she developed a close bond with another prostitute, Kiyo, and formed a genuine romantic connection with a man named Tetsuya, who wished to free her. Tsuyu arranged for Kiyo to escape with Tetsuya, but Kiyo, overcome by jealousy, betrayed them to the brothel owner. This led to the murder of both Tsuyu and Tetsuya, with Tsuyu's body discarded into a river. Her remains merged with the bones and spirits of other similarly wronged women, transforming her into the yokai Hone Onna.

As a yokai, Hone Onna initially wandered near villages seeking human companionship, but her inability to control her skeletal form caused others to flee. She was eventually found by Ai Enma, who offered her a role as a companion. After initial hesitation, Hone Onna accepted and became the third member of the team, notably the first among them to have been human.

Hone Onna typically maintains the appearance of an attractive woman resembling her human self, Tsuyu. She often wears traditional Japanese clothing, most commonly a blue kimono with a dark blue border, a red obi tied in the front, and white jika-tabi footwear. Her hair is long and black, usually styled in a traditional updo secured with a decorative clip and accessories. Across different story arcs, her primary kimono changes color and pattern, such as a white kimono with blue accents or a blue kimono with yellow and red borders. For undercover investigations, she adopts modern attire like a light brown jacket with a gray top and black skirt or a magenta jacket and skirt set, often wearing her hair down or in a ponytail. Her supernatural form reveals a skeleton, which she can expose partially or fully to intimidate targets.

In personality, Hone Onna exhibits a mild and composed demeanor. She shows more concern and sympathy for humans compared to the other companions. She becomes annoyed when referred to as an "old lady," a term frequently used by another companion, Kikuri. She maintains a cooperative relationship with all team members but displays a recurring dislike for Kikuri.

Hone Onna possesses several supernatural abilities. She can travel between the human world and the Realm of Eternal Twilight. She magically changes her attire for investigations and can create illusions to manipulate memories, making people believe she is someone familiar. Upon Ai Enma's request, she transforms into a dark red straw doll with a red string around its neck. Her primary defensive and intimidating ability is to expose her skeletal form, often using her bone fingers to penetrate human flesh. She is also skilled in throwing knife-like objects enveloped in blue spiritual fire, which engulf and burn targets upon contact.

Following the death of Ai Enma in one story arc, Hone Onna temporarily left her role and worked as a bartender. She was later recruited again after Ai's spirit signaled her return, leading Hone Onna to serve as a gym teacher at a school in Saigawara City. During this time, she and another companion, Ichimokuren, refused to assist the temporary successor, Yuzuki Mikage, and instead investigated the departure of a key human character, suspecting deeper motives. Hone Onna resumed her position as a companion upon Ai Enma's return to the role of Hell Girl.

Her abilities include a form of immortality as an undead entity, and she possesses superhuman stamina. However, a permanent end to her existence could be achieved through the erasure of her soul.