Spirit of Fire

The Spirit of Fire is a elemental spirit. In the manga and anime series Shaman King it is primarily associated with the Hao Asakura, its master.

About
The Spirit of Fire is one of five powerful elemental spirits known as the Godaiseirei. They are derived from the Great Spirit itself, and like it, constitute a collective of souls. They can be controlled by their respective Elemental Warrior, or a shaman of extraordinary power (like Hao). The power of the Godaiseirei is unmatched by any other spirit, except for maybe the Great Spirit itself.

The Spirit of Fire has the ability to consume other souls and spirits in order to further enhance its own power. Its primary medium for its over soul is the element of air, which allows Hao to manifest the Spirit of Fire with incredible speed. However, it also has the ability to transform itself into the different five elements through the doctrine of the five phases, which is made possible through Hao's mastery of said elements.

History
500 years before the start of the series, Hao was reincarnated as a member of the Pache tribe, the organizers of the Shaman Fight. Although he would fail to become the Shaman King, he succeded in the stealing from the tribe, the Spirit of Fire, which became his spirit ally when he was again reincarnated 500 years later. Its power was greatly diminished because of its journey back from Hell (where Hao negotiates the terms of his reincarnations with Taizan Kuzun, the god of the dead), forcing it to regain its strength by consuming other souls and spirits. Together, the two were an unstoppable force that was all but destined to win the Shaman Fight.

In the manga, Hao discards the Spirit of Fire after the other competitors forfeit the Shaman Fight, making Hao the Shaman King and the inheritor of the Great Spirits. The Spirit of Fire then became the spirit ally of Lyserg Diethel, its destined Elemental Warrior.

O.S. "Spirit of Fire"
O.S. "Spirit of Fire" (O.S.スピリット オブ ファイヤ) Description: This is Hao's primary Over Soul. Using his furyoku, Hao manifests the Spirit of Fire, one of the five great spirits of nature, onto the physical plane by integrating it with the oxygen in the atmosphere. Using Onmyōdō magic, Hao can alter the nature of the S.O.F. (Spirit of Fire) into any of the other five basic elements of Onmyōdō magic.
 * Shaman: Hao Asakura
 * O.S. Type: Spirit Type
 * Spirit Ally: The Spirit of Fire (spirit of nature)
 * Medium used: Oxygen

O.S. "Spirit of Fire. Black Fowl"
O.S. "Spirit of Fire: Kurobina" (O.S.スピリット オブ ファイヤ:黒雛) Description: This is Hao's armor-type O.S. which transforms the Spirit of Fire into a high-speed jet armor. With it, Hao is capable of high-speed flight and its wing-like manipulators act as appendages for close-range combat. Mounted on the back are two high-intensity laser cannons, which can incinerate anything it targets within seconds. As with most Armor-type O.S., this form requires little of Hao's furyoku, but, because of the Spirit of Fire., consumes a considerable amount of reiyoku. however, it offers capabilities which far surpasses that of the normal Spirit of Fire. in its Oversoul mode. The only foreseeable drawback is the expensive furyoku consumption
 * Shaman: Hao Asakura
 * O.S. Type: Armor Type
 * Spirit Ally: The Spirit of Fire
 * Medium used: Oxygen

Anime/Manga Difference
In the anime, Hao would ultimately deem the Shaman Fight to be a pointless contest, and would move to acquire the Great Spirits by force. After fighting through various obstacles, the Spirit of Fire would seemingly consume the Great Spirits itself, being reborn in a golden hue ten times its previous size. With their newfound power, Hao and the Spirit of Fire would defeat any and all challengers except for Asakura Yoh, who would defeat the duo with the combined might of every shaman, friend, and ally present.