Generally speaking this technique is divided into three categories: Spirit-types, Weapon-types, and Armor-types. The classification doesn't necessarily mean it will be more effective than a lower-class, just more difficult to sustain, making the overall effectiveness largely based on individual talent.
This technique enables user to integrate akashic templates into their body, forming a "unity" of both, their spirit and that of the template. The user will enter a simi-trance as they use their body as a prism for the Akashic plane gaining all the knowledge and experience of past lives. This enables one to perform task, styles, and techniques that would normally take years.
The technique also calls for a focused mind. This is a fusion of two personalities so regardless what you do there will be some bleed off, but the level of control some one has determines the amount. However if you lose control one of three things can happen:
Possession – User is overwhelmed by the templates psych and begins to start taking on aspects of their personality. A worse case scenario is that user becomes completely possessed by the template and loses themselves completely. This is incredibly dangerous as there is no telling what the template will do once it gains access to users body, and while the nature of Hyoi Gattai means that they will have knowledge of what is going on it is completely up to them what to do, because they now have full control of your body.
The void – This is caused when user is overwhelmed not by the akashic template but by the akashic energy itself. Once again user’s personality is affected becoming very stoic and introverted personality, preferring simple body language rather than speaking. When prompted they will do so in a very concise manner, always speaking in a monotone and displaying a dispassionate expression. There are benefits however in that it grants user a very rational though process this does seem to make it difficult for them communicate with others. Though seemingly cold and devoid of emotions at first glance, for those that knows them it easy to see otherwise, although the unchanging facial expressions make it near-impossible to discern those emotions.
Chaos – While the void is caused by losing control the energy utilized in an akashic template this is caused by losing control of the technique entirely. Unfortunately user doesn’t lose their connection to the akashic plane itself. This leads to user’s body becoming a sort of filter system as it begins channeling akashic energy similar to how it channels ki. This leads to a plethora of personalities fusing together to form a chaotic whole. It has been described as going into a deep sleep. The major difference between this and the other two is that while they still leave user in control this creates an entirely new individual totally independent of the user. The personality of the new individual has many different facets, which is obviously connected to their connection to the akashic plane. They alternate between melancholy and incredible optimism, often unpredictably. Their behavior is considered eccentric, acting with what may be called determination, persistence, or resourcefulness by some and ruthlessness and hyperactivity by others. Surprisingly this is the most stable since there is no single will to concentrate on you have much less stress on the body, so you get more power. Unfortunately user has absolutely no control or knowledge of what’s going on.
While this variation of Hyoi Gattai allows for stronger and smoother movements the time user are able to keep it up is directly proportional to the strength of the body. I.E. the stronger user is the longer the connection last. This is because of stress it places on the body.
Weapon-type manifests the template in a symbolic offensive form, enabling the template to directly display their natural fighting capabilities as a weapon, but this type is requires great talent to wield effectively.
Armor-type manifests the template through wielders actual clothing.
The unity type is a fusion of the spirit type and weapon type of the Hyoi Gattai where user’s body is used in luau of a weapon. It is very difficult to pull off since both the template and the user must be synced the entire time the technique is used. When using this ability, they essentially combine their human form and the template, incidentally increasing their power considerably.
Musō Tensei (無想転生, Nil-Thought Rebirth): The ultimate secret technique of Hokuto Shin Ken. It is said that only one who embraces the true nature of sorrow can awaken its power. Kenshirō was the first man in Hokuto Shin Ken's 1800 year history to learn Musō Tensei during the epic struggles against his friends and great rivals. Musō Tensei allows the user to achieve a state of "nothingness", impervious to physical attacks, and commune with the souls of fallen rivals.
These techniques are shamanistic in nature. Shamanism involves working with spiritual energies, communing with spirits and plane travel, all of which if combined into a martial arts system would be quite formidable against a foe who only knows how to fight upon a purely physical level.