Reiryoku

is a power aligned with the spiritual sensitivity and willpower of the user. It is used by Shinigami and other spiritual beings to provide power for their various abilities.

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 Reiryoku 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 souls in Soul Society with very high levels of Reiryoku who receive special training to utilize their powers. Hollows and other spirits use their Reiryoku to catch their prey.

Sensing Reiryoku
Another basic ability that beings with higher-than-average levels of Reiryoku possess is the ability to sense 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 in the form of Reiatsu, which can be sensed. This ability apparently requires some innate skill, but can be increased with training. Initially, Ichigo Kurosaki's ability to sense the spiritual energy of others was very poor, but gradually grew much more proficient in it, even being able to use various high-level techniques to locate or detect particular people, such as his close friends.

Every spiritual being has a unique pattern to his/her emitted Reiryoku. One can recognize the pattern of their 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 (i.e. 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 Visored are a special case, because when their Hollow mask is donned, their pattern of Reiryoku resembles that of a Hollow, rather than that of a Shinigami.

There are a few possibilities to block Reiryoku. One is the usage of Sekkiseki, a special kind of stone that completely blocks Reiryoku from both sides. The walls of Seireitei, and the walls of the Senzaikyū are built from this stone. As Sekkiseki 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 Senzaikyū.

Another means of blocking Reiryoku is a special garment invented by Kisuke Urahara, which completely hides any emission of Reiryoku coming from the wearer, enabling him/her to escape from somewhere or approach someone while being impossible to notice via sheer sensing of Reiryoku.

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 Reiatsu (霊圧, Spiritual Pressure), is considered a show of force, a means of intimidation or can even be an attack in itself. 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 need food to replenish their strength, while on the other hand, the regular souls that dwell in Soul Society that do not use their Reiryoku do not need to eat.

For high-level Shinigami, such as Captains and Lieutenants, their spiritual pressure is so high, they can cause undesirable ripples in the Human World. As such, a seal is automatically placed onto them whenever they pass through the Senkaimon from Soul Society to the Human World, limiting their strength to 20% of their maximum output. Under critical situations, such as the battle against the Espada, the seal is not applied even when the Captains and Lieutenants pass through the Senkaimon.


 * Aside from Spiritual Pressure, Shinigami and Visored generally use their Reiryoku to
 * cast Kidō spells
 * increase their speed (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 laser-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.


 * Quincy can also increase their mobility, and form a weapon (usually a bow) with their Reiryoku. 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 Reiryoku in various special items.