Wanyuudou serves as Enma Ai's assistant and takes on multiple forms depending on the situation. Most recognizably, he becomes the black straw doll with a red string tied around its neck—a detail fans often connect to the red scarf he wears in human form. When Ai travels to the human world to claim a soul, he transforms into a massive flaming wheel that appears on her coach, which is marked with the same black flame-crest that brands those who've made a contract with Hell Girl.
In his human guise, Wanyuudou looks like a mild-mannered older man who keeps his eyes mostly closed, wearing a fisherman's hat and traditional Japanese clothing. Despite this gentle appearance, he's actually skilled in martial arts. His name literally means "a wheel entering the road," a direct reference to his flaming wheel form.
Wanyuudou's backstory goes back to the Samurai era, when he worked as a driver for a princess's entourage. He failed to protect them during a tragedy that killed everyone under his care, and the guilt transformed him into a youkai that haunted people as a burning wheel. When Ai eventually freed him from this curse, he became deeply indebted to her—so much so that he's stated he and his two colleagues owe her a grave debt for saving them from falling into Hell itself.
Content compiled by AnimeList.moe from publicly available sources.
