Originally, humans were thought to have gained their special ability simply by being in the presence of a large amount of spiritual energy, thus birthing their own unique ability in order to combat such a threat against them, similar to an antibody developed in order to fight against disease. Although this is not exactly the case, it isn't too far from what actually happens. While it is true that humans gain their abilities from being near a specifically large source of reiatsu, the type of reiatsu that they have been around can also be a factor in what abilities they may achieve at a certain point in time. The different energy sources are known collectively as Crystallizations, and a different Crystallization can effect the way a human grows spiritually. Aside from being near these species enough to gain their reiatsu boost, if a human's parent is of these species, there is a very high chance that they gained a Crystallization through them, although this is not always the case.

Crystallization functions in a very simple way. As the subject in question is around the species while developing their abilities, their reiatsu would be constantly assaulted with the other's reiatsu. Slowly, this reiatus would begin to be absorbed into the user's own reiatsu in an effort to combat it, similar to a snake charmer or scorpion/spider handler allowing the creature to bite them and raise their resistence to the poison. After enough reiatsu has permeated the body of the user, it stabilizes within them as their true power source, and becomes the Crystallization. Due to this, they would have a natural affinity for that race, and possibly even emit traces of the species reiatsu in question.

Shinigami Crystallization: By being around shinigami long enough in order to develop their abilities, a human may have achieved Shinigami Crystallization. Shinigami Crystallization allows for a human to obtain a greater chance of becoming a shinigami after death (if they are soul burial'd, of course), and retain their memories or abilities. Through enough training with a shinigami, this may also allow the human in question to learn Shunpo.

Hollow Crystallization: By being around hollow long enough in order to develop their abilities, a human may have achieved Hollow Crystallization. Hollow Crystallization allows for a human to obtain a greater chance of hollowfication after death, the waiting period cut nearly in half compared to a regular soul. This will also allow for them to keep their memories and abilities after death if they so choose (to some degree, at least). Enough training with hollows could potentially allow for a human with hollow Crystallization to learn a very basic cero, or garganta with enough training by a Hollow.

Vizard Crystallization: This Crystallization can be achieved three ways, but is the most rare. If a human is either A.) Around a vizard while unlocking their abilities, B.) The son or daughter of a vizard, or C.) Around a shinigami and hollow of equal amounts while unlocking their abilities, they may have obtained Vizard Crystallization. Vizard Crystallization allows for the human to have a greater success rate at beating down their inner hollow in the generations to come if they ever have the option to become a true vizard. It also allows for the human to learn shunpo AND a cero or garganta with enough training by a vizard.

Arrancar Crystallization: This too is one of the rarest Crystallization's to have achieved. It requires for a human to have been around a great source of arrancar reiatsu while they were unlocking their abilities. If they have achieved this Crystallization, it will allow for them to gain the option of becoming a natural arrancar after death. While alive, they may have the potential to learn Sonido with enough training by an arrancar.

Human Crystallization: By being in the presence of large amounts of natural, human reiatsu will allow for a human to achieve a 100% natural Crystallization to them -- The Human Crystallization. If a human obtains the Human Crystallization, they will remain more youthful in their age then most people. It also allows for them to obtain greater prowess with their unique ability, seeing as there is no 'taint' to hold off growth. Very rarely, a Human Crystallization will allow for it's host to undergo a reincarnation cycle.

Quincy Crystallization: Due to the quincy being practically extinct, this Crystallization is damn near a legend. While having been in the presence of a quincy while unlocking their abilities, a human will unlock the Quincy Crystallization. This will allow for one of two things for them. The first is to reject their abilities and become a quincy at any point in time. The second is to remain human. By remaining human and training diligently with a quincy, they could potentially learn Hirenkyaku.

Hybrid Crystallization: If someone has been in the presence of equal amounts of different types of reiatsu while undergoing their crystallization stage, it is possible for these reiatsu's to merge and condense inside of said individual, creating a Hybrid Crystallization (unless it is specifically Shinigami and Hollow reiatsu, which would yield a Vizard Crystallization). Hybrid Crystallization is different then any other Crystallization, solely because it does not give any particular boosts relevant to a single species. Instead, Hybrid Crystallization will allow for the user to always free itself from any taint on their reiatsu that was inflicted solely by the species' which makes up it's Crystallization. This means they cannot be controlled or manipulated by the species that has given them their crystallization.


What happens if a Human has a certain crystallization but becomes a different species then their crystallization intended?

If a human had a hollow crystallization but became a shinigami, or something along the similar lines (such as shinigami crystallization but later became a hollow), their crystallization would still be present. It would not remain the same, however. The crystallization would warp and change, becoming something new entirely, yet still have the same effects.

Negative Crystallization: If one possessed a specific crystallization but became a species unintended for by the crystallization, their crystallization would warp into this. The negative crystallization actually manifests itself as a physical object somewhere on the person of the new species, specifically as a tattoo. This tattoo is a "get out of jail free" card. The negative crystallization, once offered a blood sacrifice by the host, will revert the owner back into their basic human form with their original crystallization. It will effectively repel and extinguish the new species' dna and reiatsu from their system, as well as abilities.

If you have achieved a particular level of skill with your particular crystallization and unique ability gained from it, you will unlock the potential of Perfect Crystallization. By condensing and focusing the abilities you possess, you can reach new heights in power and skill. Perfect Crystallization is actually influenced by the particular types of crystallization in a slight manner.

Perfect Hollow Crystallization - This transformation usually yields a more beast-like form. Usually, weapons are disregarded in this transformation, although some have been known to have continue using them. More likely then not, a Perfect Hollow Crystallization will allow for the user to either possess a hollow mask or hollow hole, although this is not always the case. The mask is usually very basic, plain white with barely-defined teeth.

Perfect Shinigami Crystallization - This transformation is usually very minimal and involves perhaps a wardrobe shift and perhaps minor cosmetic changes. This transformation actually develops the inner workings of the ability more then the user itself. Some have been known to possess a zanpakuto-like sword in this form.

Perfect Vizard Crystallization - This transformation is similar in the like of both hollow and shinigami perfect crystallization, although both are watered down, it still develops their physical body as well as abilities to varying degrees. Some have been known to attain both a sword and mask/hole in this form.

Perfect Arrancar Crystallization - This transformation always provides the user with a hollow hole. There are no exceptions. Aside from that, the transformation will help the user develop their physical body and abilities similarly to Vizard Crystallization.

Perfect Human Crystallization - This transformation is completely unique to the user. There is no average between physical body and abilities, like shinigami and hollow. Because of the pure uniqueness of this, there is nothing standard gained.

Perfect Hybrid Crystallization - This transformation is completely unique to the user. There is no average between physical body and abilities, like shinigami and hollow. Because of the pure uniqueness of this, there is nothing standard gained.