Spiritual Energy

Spiritual Energy or Reiatsu 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. Reiatsu 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 Reiatsu into the air. The aforementioned ability is known as Spiritual Pressure, possessing power that could be literally felt within the atmosphere.

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

Sensing Spiritual Energy
Another basic ability that beings with higher-than-average levels of Spiritual Energy 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 Spiritual Energy, which can be sensed. This ability apparently requires some innate skill, but can be increased with training. Ichigo Kurosaki can sense the spiritual energy of others very poorly, but he gradually becomes more adept in this skill.

Every spiritual being has a unique pattern to his/her emitted Reiatsu. 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 Reiatsu 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 Spiritual Energy pattern of Hollows for example is easily distinguishable from that of Pluses or a Shinigami. Vizards are a special case, because when their Hollow mask is donned, their pattern of Spiritual Energy rather resembles to that of a Hollow, in contrast to that of a Shinigami.