Wanyuudou, a tsukumogami born from a royal carriage wheel shattered during a wartime ambush over four centuries ago, emerged when fire arrows destroyed the vehicle, sending it over a cliff and claiming the lives of a princess and her entourage. The sole surviving wheel, steeped in anguish, evolved into a flaming entity with a human visage, haunting the cliffside until Ai Enma offered redemption through a human form and enduring partnership. This alliance established him as her most trusted aide across every season of the series and its live-action adaptation.

In human guise, Wanyuudou manifests as a composed elderly man with a bald head, half-lidded eyes, and traditional attire: a dark haori, yukata, and a light gray fedora. His wardrobe subtly shifts from a red scarf in earlier seasons to a brown haori and dark gray yukata later. He alternates between this form, a blazing wheel, and a black-and-red hell-marked carriage to ferry Ai during missions. When invoked by Ai for vengeance, he takes the shape of a black straw doll bound by a crimson neck cord.

Exuding calm wisdom laced with dry wit, Wanyuudou prefers diplomacy over conflict yet harbors profound supernatural knowledge, often uncovering truths ahead of others. His serene exterior belies formidable combat prowess and superhuman strength—evident when he halted a plummeting truck barehanded. Mastery over flames, vehicle possession, illusion-crafted memory alteration, and traversal between the human realm and the Realm of Eternal Twilight underscore his capabilities.

After Ai’s temporary demise in *Three Vessels*, he assumed mortal roles as a construction laborer and school janitor until Kikuri enlisted him to aid Yuzuki Mikage, Ai’s interim successor. His brief service to Yuzuki highlighted unwavering loyalty, culminating in a return to Ai upon her resurrection. Though adaptable to leadership shifts, his strained rapport with Kikuri reveals layered alliances within their circle.

Centuries of torment as a vengeful spirit, rooted in failing to protect the princess, found solace through his bond with Ai. Bound to her mission, he occasionally revisits fragmented memories, such as ancient hot spring sojourns with her. His name, signifying “wheel entering the road” or “wheel monk,” echoes his origin and enduring role as a bridge between worlds.