Beast Fusion is an ancient technique involving humans and guardian spirits. It involves the human physically and mentally merging with their guardian spirit partner, thereby taking on physical attributes of their guardian spirit and being able to channel that spirit's specific powers using their own body as a living medium. It is the most powerful guardian spirit technique and anyone capable of mastering it is said to become a master of guardian spirits. However, it is no easy task as the mastering of Beast Fusion requires a resilient mind and body and a strong compatibility with their spirit partner.
Beast Fusion is a technique that is incredibly difficult to master because it is the most powerful technique humans and guardian spirits can achieve in unison as well as the amount of strain it puts on both individuals' mind. In order to even barely execute Beast Fusion, the human and spirit participants must have a strong attunement with each other. If a human and spirit are incompatible with each other, their chances of a successful Beast Fusion severely drop and are likely to end with disastrous results while two that are a highly compatible are more likely to succeed and maintain the merging. Partnership is essential for Beast Fusion as cooperation and good compatibility are the prime focus for achieving an optimal Beast Fusion.
Fusion has only ever been attempted with a single guardian spirit, as it is unsure what would occur if more than one spirit was merged with a human host, though many assume the results would be catastrophic as the human mind would not be capable of taking on a third mind in the merging.
Fusion generally appears different for each person and spirit as each individual is different and possesses a different level of attunement with a specific spirit. Essentially, one spirit merged with one human may appear a certain way while the same spirit merged with a different human may appear differently due to the differences in personality and compatibility with their human hosts.
Beast Fusion differs from usage of weapon transformation in the sense that it is much more powerful and requires more concentration and focus than maintaining a guardian spirit's weapon form. There is no mental or physical merging in weapon form usage, making it much easier to handle than Beast Fusion, which requires both a strong body and resilient mind.
When merged, the human partner takes on physical - often heavily armored - traits of the guardian spirit with whom they are fused with. These usually include features such as wings, ears, tails and any armor the guardian spirit is equipped with. The fusion is not just physical, but also mental as their minds become one. The nimble and supple physiology of the human body makes them excellent hosts for guardian spirits. Humans with strong minds and bodies will easily be able to take in a strong spirit, allowing said spirit to achieve it's maximum potential through their human host. Essentially, this means that guardian spirits are far more powerful working in tandem with a human partner or host. The human partner inherits all of their spirit partner's strengths, abilities and attack capabilities and are able to execute them in a far more focused and concentrated manner. Beast Fusion heightens focus and coordination, however, there are drawbacks.
While the human partner will inherit the spirit's strengths through the merging, they will also inherit all their weaknesses as well, though some may be countered by human physiology. For example, many water spirits are often confined to an aquatic environment due to their physiology, but this weakness is canceled out by human physiology. However, other weaknesses, such as elemental weaknesses, will remain regardless.
In addition to this, there are also potential physical and mental damages that can occur to both parties. Prolonged merging can cause the human partner to begin taking on the animal instincts of their partner, rendering their minds feral and chaotic focused only on fighting and destruction. In addition, inexperienced users can lose control and end up going berserk, attacking everything in sight. The only way to stop the rampage will be to forcibly separate the human and spirit from each other, a difficult task that can result in great damage to both human and spirit, and in some cases, death. Should a human and spirit remain bonded for too long, they will be unable to separate and will be rendered a mindless, rampaging force. Even for individuals with strong compatibility, prolonged merging is still not recommended as even with strong compatibility, they are still susceptible to losing their minds to the spirit's feral and animalistic natures. In essence, merged individuals with strong compatibility have a much less chance of losing control and being unable to separate than those with weak compatibility.
Aside from a regular Beast Fusion, there exists three variations of the technique: Partial, Chaos and True.
A Partial Beast Fusion differs from a normal Beast Fusion in the sense that it is only half of the technique. There is no mental link between the two parties like in a full Beast Fusion and as a result, the potential for power loss and loss of control is greatly reduced. Elemental abilities are still inherited by the human host, though at a reduced power level. In addition, the human host will still take on traits of their guardian spirit partner, however this is only restricted to ghostly, ethereal appendages such as wings, claws, tails and horns that are not completely physically connected to the human.
Many use Partial Beast Fusion as a stepping stone to mastering a full fusion because it requires less focus and energy to maintain, there is little chance for one to lose control and it is highly efficient. However, when compared to a full fusion, Partial is still much weaker in terms of power. In addition to this, because Partial does not mentally link both parties, disagreement between or low compatibility can result in decreased coordination, which can easily be taken advantage of by a cunning opponent.
Chaos Beast Fusion is a destructive variation of a full Beast Fusion which can result from a number of ways. Most commonly, a Chaos Beast Fusion can result from prolonged execution of a regular Beast Fusion, turning the bonded pair into a rampaging, feral monster. Alternatively, Chaos Beast Fusion can result from a forced fusion between two individuals with low compatibility. This results in an unstable fusion with an even more unstable mental link. The only way to stop a Chaos Beast Fusion is either death or forced separation, which can result in death or permanent mental and physical damage.
A Chaos fusion is characterized much like a Beast Fusion with more inconsistencies and chaotic features among physical appearance as well as blank eyes.
True Beast Fusion is the highest and most powerful level of Beast Fusion that can be attained. Their appearance is often quite regal and imperial surrounded by a powerful aura. A True Beast Fusion can only be attained when both the human and guardian spirit are in perfect synchronization with each other. They become one mind, one body and one essence and there is little chance of power loss unlike with a normal Beast Fusion. This results in heightened powers and new techniques available to the user. If two parties attempt a True Beast Fusion while not in perfect synchronization with each other, it may result in a Chaos Beast Fusion.
In order to reach perfect synchronization, a human and guardian spirit must attain a strong, intimate bond with each other. There can be no doubts or fears between the two as such negative emotions can compromise their attunement. They must maintain a calm demeanor in order to connect their mind and body. If the synchronization is broken even slightly - possibly due to fear, doubt, bickering or even stress - the Beast Fusion will collapse on itself and break. It only takes one of the bonded pair to fall out of sync for the entire fusion to break apart.
- The concept of Beast Fusion is based on Shaman King.