Wanyuudou serves as the primary companion to Ai Enma. His existence began over 400 years ago as the left wheel of a royal carriage. During a wartime escape, attackers struck the carriage carrying a princess and attendants with fire arrows, causing it to plummet off a cliff. The burning left wheel survived, transforming into a tsukumogami – a flaming wheel spirit bearing a human face. This form haunted the cliffside nightly, terrifying travelers and gaining a reputation as a vengeful spirit among nearby villagers. Ai Enma encountered him during her travels and invited him into her service. Accepting, he gained an ageless human form: an elderly man with narrowly opened eyes, traditionally dressed in a haori and yukata, and consistently wearing a fedora hat and red scarf. Typically calm and mild-mannered, he displays considerable knowledge and wisdom regarding supernatural matters. He exhibits reluctance toward aggression and maintains composure in tense situations. Despite his reserved nature, he occasionally jokes, smiles frequently, and habitually smokes. He demonstrates loyalty and fondness toward Ai and other companions but consistently shows dislike toward Kikuri. His key abilities include transformation into a black straw doll adorned with a red string (representing his scarf or hat tilt), his original flaming wheel form, or a full black-and-red carriage bearing the hell-bound crest. As a carriage or wheel, he transports Ai between realms while levitating. He manipulates fire to ignite objects or project fireballs and possesses mechanical wheels or vehicles to control them. Additional capabilities include traveling between the human world and the Realm of Eternal Twilight, altering clothing illusions, manipulating memories to assume false identities, and employing considerable martial arts strength – demonstrated when he stopped a falling truck. Following Ai's temporary death at the end of the second season, he lived peacefully as a construction worker. Kikuri later recruited him back into service upon Ai's return. During the third season, he worked as a school janitor in Saigawara City to observe clients. When Yuzuki Mikage temporarily became the Hell Girl, he aided her independently before returning to Ai after she resumed the role.