An Over Soul can best be described as a metaphysical construct that fashions an apparition in elaborate and complex shapes by a shaman using their Furyoku and a medium. Aside from gaining corporeal properties, an Over Soul actualizes the knowledge and memories of an apparition and allows their memories to manifest essentially as magical powers, allowing for feats such as spellcasting or paranormal effects. Being that an O.S. is composed entirely of a shaman's Furyoku, there is no actual matter. An Over Soul can only be damaged by another, this renders all form of conventional weaponry useless, as there is no actual substance to interact with. While any spirit can be molded into an Over Soul, their attributes depend solely upon the spirit's ego—or identity. Depending on its ego, the ghost can be molded by the shaman into any shape or form the shaman desires, enabling the direct display of its abilities to protect the shaman.
Human ghosts usually make poor choices for an Over Soul, as opposed to animal spirits, due to their egos but can evolve over time into higher spirits—spirits whose souls have been refined over hundreds of years and have attained their purest form. While the exact design of an Over Soul depends entirely on the shaman's imagination, it is also important that the shaman chooses a medium which is symbolic and best symbolizes the spirit's abilities, such as a katana for Amidamaru who is a samurai.
In regards to strength and integrity, an Over Soul's durability is proportionate the amount of Furyoku utilized, as well as the shaman's level of concentration. It is important that a shaman to keep in mind that although the mass of an Over Soul remains constant, Furyoku is consumed anytime it is used to create matter, like ice, which consumes Furyoku in itself. Furyoku is only consumed when the "body" of the Over Soul is compromised. At this juncture, the Over Soul must be immediately infused with the appropriate amount of Furyoku necessary to maintain its integrity, depending on the degree of damage sustained. If an Over Soul absorbs enough damage, it breaks and dissolves along with all Furyoku used in its creation. Therefore, a shaman must consider how much Furyoku to charge their Over Soul with during each engagement.
The sizes and shapes of certain character's O.S. often change since their introductions, some without any explanation. This could be attributed to the mental imagery a shaman uses to envision the form, size, and ability of the Over Soul. Yoh's Spirit of Sword, for instance, has changed considerably throughout the series since its introduction in volume 15 of the manga, with a defined blade and the inclusion of a large hilt.
Spirits themselves have three sub-categories:
- Ghost-type: Normal-class spirit ally
- Seirei-type: Sacred-class spirit ally
- Kami-type: God-class spirit ally
Types of Over Souls
Generally speaking, O.S. can be divided into three categories: Spirit-types, Weapon-types, and Armor-types. Strictly speaking in terms of practicality, the classification of an O.S. doesn't necessarily determine its effectiveness in live combat, but the higher the quality of the O.S. determines its range of abilities and maintenance, making the overall effectiveness of any O.S. largely based on the shaman's individual talent.
Spirit-type Over Soul
- These O.S. usually manifest an apparition corporeally in such a manner as to fully utilize its unique abilities. (ie. O.S. Bason, O.S. Kororo-Snowboard).
Weapon-type Over Soul
- These O.S. manifest an apparition as a supernatural instrument or armament (ie. O.S. Spirit of Sword, O.S. Kororo-Ikupasuy, O.S. Super Bushin), usually to compliment the shaman's personal fighting style.
Armor-type Over Soul
- These O.S. are the most efficient form of Furyoku-based constructs. Armor-types represent the pinnacle of O.S. magic and are the most practical type of O.S. because of their resilient, highly dense Furyoku composition. This method makes them equally formidable in terms of raw power.
- Also known as "Over Soul Merge", these O.S. are very difficult to achieve due to various factors. Unity-types require both the shaman and their apparition to establish and maintain continuous spiritual synchronization throughout the entire process, which is the sole responsibility of the Shaman. The major advantage of the Unity-type is the unrestricted access to an apparition's nature abilities. The only example of this is Chocolove McDonell's Black Jaguar O.S. with Mic the Jaguar.
- Shaman King Manga - Chapter 29
- Shaman King Manga - Chapter 28