Reiryoku

Reiryoku (霊力, Spiritual Power) is a power aligned with the spiritual sensitivity and willpower of the user. It is used by Shinigami to provide power for their various feats and to effectively channel the powers of their Zanpakutō. It can also be used to cast Kidō, magic spells created by the Shinigami. Reiryoku can even be coalesced into a physical form and thrown or shot as a projectile. As a display of potency, spiritual beings have the ability to incapacitate the opponent's movement and simultaneously frighten them, by means of dispersing Reiryoku into the air. The aforementioned ability is known as Reiatsu (霊圧, Spiritual Pressure), possessing power that could be literally felt within the atmosphere.

Overview
Every spiritual being and every human has a certain amount of Reiryoku. If this amount is higher than a certain degree, it grants the person superhuman abilities. Those with such an above-average level of Spiritual Energy are very rare among living humans. It seems to be that the most basic ability that humans with a higher level of Reiryoku have is the ability to see ghosts: Pluses, Shinigami and Hollow alike. Shinigami are essentially departed souls in Soul Society with very high levels of Reiryoku who receive special training to utilize their powers. Hollows, if they make active use of their Reiryoku, usually do it to catch their prey or to evade Shinigami more effectively, the extreme case being the Arrancar, who have an amount of Reiryoku equal to Shinigami, and are able to use it just as efficiently in combat.

Spiritual Power
This level of spiritual power corresponds to those possessing an average level of spiritual power. This level of power is common among those of significant spiritual awareness and may even possess powers of their own but the power levels can vary among individuals. This is also a common level of power for a regular seated and non seated member of the Gotei 13 or lesser power individuals.

High Spiritual Energy
This level of spiritual power corresponds to those possessing an above average amount of spiritual power, which is finely controlled. This level of spiritual power is common amongst those of an average lieutenant rank.

Great Spiritual Energy
This level of spiritual power corresponds to those possessing a large amount of spiritual power which is finely controlled. This level of spiritual power is common amongst those of an average Captain rank.

Immense Spiritual Energy
This level of spiritual power corresponds to those possessing a huge amount of spiritual power which is finely controlled. This level of spiritual power is reflected in its ability to enhance a user during combat as well as its ability to affect the surrounding environment on a controlled level, allowing the wielder to use it in combat to startling degrees.

Vast Spiritual Energy
This level of spiritual power corresponds to those possessing a huge amount of spiritual energy which is wild and untamed. This level of spiritual power has a possible tendency to leak from a person or when released can affect the surrounding area in a destructive way. Those of this level have no real masterful control over their spiritual power, as it can effect those around them unintentionally.

Sensing Reiryoku
Another basic ability that beings with higher-than-average levels of Reiryoku have that they are capable of sensing other spiritual beings without relying on their five basic senses. This is possible because every spiritual being emits a certain amount of his/her own Reiryoku, which can be sensed. This ability apparently requires some innate skill, but can be increased with training.

Every spiritual being has a unique pattern to his/her emitted Reiryoku. One can recognize the pattern of his friends and acquaintances after some time, being able to sense their presence and their physical and mental state from relatively great distances. Sudden changes in Reiryoku pattern can mean that the person in question is in great stress (e. g. fighting) or has received a grave wound.

Different types of spiritual beings have greatly different patterns, the Reiryoku pattern of hollows for example is easily distinguishable from that of Pluses or a Shinigami. The Vizard are a special case, because when their hollow mask is donned, their pattern of Reiryoku rather resembles to that of a Hollow, in contrast to that of a Shinigami.

There are a few possibilities to block Reiryoku. One is the usage of Death Stone, a special kind of stone that completely blocks Reiryoku from both sides. The walls of Seireitei, and the walls of the Tower of Punishment are built from this stone. As Death Stone blocks even the strongest Reiryoku emissions, it does not just inhibit the sensing of one's Reiryoku pattern, but effectively closes out most unwanted visitors in the case of Seireitei, and prevents the escape of even the strongest prisoner from the mentioned tower. This stone also prevents the ability to gather Reishi underneath your feet to walk in the air whist within Seireitei.

Controlling Reiryoku
The aforementioned emission of Spiritual Energy is a common and natural phenomenon, but a spiritual being can also control the degree of this emission, this usually requires a certain amount of skill and training. By completely blocking his/her Reiryoku "pouring out", one can completely hide his/her presence from other spiritual beings and spiritually aware humans. On the other hand, amplifying this emission is known as Spiritual Pressure, and is considered a show of force, or even an attack in itself, and it can indeed paralyze opponents, and cause direct damage to the surrounding individuals and inanimate objects alike.

Aside from controlling the amount of emitted Reiryoku, most spiritual beings and some of Ichigo's spiritually-aware human friends are capable of performing many superhuman feats with the help of their Reiryoku. These feats usually require a certain level of concentration, and they tend to tire the person after some time, or after performing some of them in quick succession. It is also known, that after excessive usage of Reiryoku, Shinigami and other dwellers of Soul Society need food to replenish their strength, while on the other hand, they do not need to eat anything to sustain themselves during everyday activities.
 * Aside from Spiritual Pressure, Shinigami and Vizard generally use their Reiryoku to
 * cast spells - see Kidō
 * increase their speed and their height of jump, or float in the air - Hohō
 * use the special abilities of their Zanpakutō
 * increase their physical strength and power
 * Hollows and Arrancar have other abilities, namely Cero and Bala, that are condensed Reiryoku fired towards the opponent. In the case of the former, it is done in a flamethrower-like manner; in the latter case, the fired Reiryoku is bullet-like. Hollows and Arrancar can also increase their mobility like the Shinigami above, and the usage of their Zanpakutō also relies on the usage of Reiryoku, albeit in a different manner. Hierro is also a move that uses an Arrancar's Reiryoku for defense.
 * Quincies can also increase their mobility, and form a weapon (usually a bow) with their Spiritual Energy. In their usage of Reiryoku however, there is a fundamental difference from spiritual beings - they primarily rely on collecting reishi from the environment, and use this collected reishi to fight. They can even collect and store Spiritual Energy in various special items.