A gigantic red oni, it is by far the most humanoid oni ever seen. It wears a white shirt and has a glowing green face on its torso. There are two known instances where one has been summoned. One has been created by Kyōyama Anna when she unwittingly used her uncontrollable Reishi power to make a Naka-Oni evolve into an Oh-Oni. Anna's Oh-Oni has shown intelligence and a personality and though it has a sadistic behavior it speaks in a calm tone and even calls Anna its mother.
After it was sent to hell, it somehow became Sati Saigan's follower and began acting in a more kind and friendly way. When Yoh is sent to train in Hell by Lady Sati, the Oh-Oni appears and leads Yoh to his training area. The Oh-Oni, together with the Cho-Oni, Asakura Yohken and Mosuke, later appeared within the Great Spirit as the escorts of Hao's mother, Asanoha Douji.
Another was summoned directly by Asakura Hana, due to the power given to him by Asakura Hao, where Hana, in a state of near-death, goes into a trance and summons various sizes of onis to defend himself. It appeared when Ichihara Ryuji almost killed Asakura Hana by fracturing his skull, where Hana began summoning oni at random to attack Ryuji and Asakura Luca. As Luca destroyed all the Onis he summoned, Hana began chanting and summoned bigger onis until finally, he summoned a single Oh-Oni that landed an attack on Luca's Over Soul before it too was destroyed. In response, Hana gathered the regenerating remains of his onis to create a Dark-Oni that was finally able to defeat Luca.
The one created by Anna was able to regenerate and evolve by feasting on other onis and spirits. After doing so, it gained a thick mustache and a pointy collar. As an oni created from at least 1080 worries, hopes, and prayers, the Oh-Oni is extremely powerful and, according to Matamune, it has the speed of an arrow and the strength of a hundred bulls. Its intelligence made it far stronger in battle and it even had a named technique where it summoned smaller onis to attack from the stump of its arm, known as Oni Drum Roll (鬼太鼓 Onidaiko). The souls within it are connected by a chain of resentment giving it an infinite power.
Due to Anna and Yoh's past never being mentioned, Oh-Oni is never seen in the 2001 anime series.
- Although never shown in the series, Hiroyuki Takei has drawn the Oh-Oni in spirit ball mode, on a piece of promotional material.
- Anna's Oh-Oni's medium were used, by Asakura Kino, to create a 1080 prayer beads.
- An Oh-Oni appears as a boss in the video game Shaman King: Master of Spirits 2. Because the game was based on the English version of the anime, in which Oh-Oni does not appear, he is colored blue, but if hit enough, he will turn red and his name was changed into "Great Ogre".
- Shaman King: Master of Spirits 2
- Shaman King Manga - Chapter 299
- Shaman King Manga - Flowers Chapter 10
- Shaman King Manga - Chapter 172
- Shaman King Manga - Chapter 176
- Shaman King Manga - Kang Zeng Bang Volume 16 Extras; Shaman File 221