Naka-Oni

The Naka-Oni (中鬼, Naka Oni) is a fictional character in the manga series of Shaman King. It was created by Kyōyama Anna's uncontrollable Reishi (霊視) powers.

Osorezan Revoir
It was created when Kyōyama Anna and Asakura Yoh went to a temple on new years day. When the prayers, hopes and worries exceeded 1080, something that easily happened during that time and place, Anna's Reishi powers went out of control and created the Naka-oni.

While fighting with Matamune when Anna's powers went way out of control, it began gathering the surrounding Oni in the area. The Oni began devouring each other and in the end, the Naka-Oni would evolve into Oh-Oni.

Anime/Manga Difference
Naka-Oni is a manga only character and never appears in the anime.