Reiatsu is the physical pressure that arises when releasing spiritual energy known as Reiryoku. Unlike Reiryoku, which is stored energy within the soul, Reiatsu is energy in active use, available for perception by other spiritually gifted beings. As a rule, the more Reiryoku a being has, the higher its Reiatsu, but skillful control over one's own energy allows one to surpass an opponent with a larger reserve but worse management.
All Shinigami have special points on their wrists through which Reiatsu exits outward. If these points are blocked, the Shinigami will burn from the inside from their own energy. Released Reiatsu usually returns to its owner, but during an explosive discharge it can capture particles of the surrounding environment, sometimes causing unforeseen consequences for the bearer himself.
The density of Reiatsu in the spiritual particles of the body determines the Spiritual Class of a being from 1 to 20, where 1 is the strongest. The Captains of the Gotei 13 belong to class 1-3, the lieutenants to 4-5. The bodies of beings of class 3 and above are too dense to naturally decompose in the Soul Society after death, so a special ritual is performed for them.
Reiatsu can have various colors, not related to race or strength, and sometimes take a form reflecting the inner essence of the owner. Among the known manifestations is the enormous skull of Kenpachi Zaraki.
The use of Reiatsu is diverse. In defense, it strengthens the bearer's body, allowing one to ignore the blows of weaker opponents, and with a significant difference in strength, to completely nullify others' abilities. Psychologically, Reiatsu can cause fear, stunning, paralysis, or even phantom pain, simply by being near the target. In offense, high pressure is capable of inflicting physical damage, creating shock waves through a weapon, or killing weak beings by mere presence.
There are several types of Reiatsu: standard (in most), double (in Vizards and Arrancars, felt as a mixture of Shinigami and Hollow), black (associated with the power of the Soul King, also called Chaos), and elemental (for example, Yamamoto's fire Reiatsu or Hitsugaya Toushirou's ice one).
