Reiatsu

is the physical force/pressure that a person’s Reiryoku creates when released. Most Shinigami and Arrancar, even Quincy and Bounts can manipulate the release of their reiatsu. 1st Division Captain Genryūsai Shigekuni Yamamoto used his spiritual pressure in the form of a stare to paralyze Nanao Ise. Yachiru Kusajishi, the lieutenant of the 11th Division can emit her spiritual pressure into the form of an angry pink cat. The most powerful Shinigami such as Ichigo Kurosaki, Kenpachi Zaraki, Sōsuke Aizen, Captain-Commander Yamamoto, Tōshirō Hitsugaya, and Byakuya Kuchiki and others have vast amounts of Spiritual Energy, which they can emit in the form of Spiritual Pressure with devastating effects.

Reiatsu VS Reiryoku
The difference between spiritual pressure and spiritual energy is simple: Reiryoku is the amount of energy a being has stored within their body or soul, whereas Reiatsu is the pressure that a person’s Reiryoku exerts. The difference is much like energy and power. Power being the amount of energy exerted per unit of time. Reiryoku is potential while Reiatsu is energy in use. In general, those with high levels of Reiryoku will often have the highest levels of Reiatsu also. A skilled warrior can overcome a person possessing greater Spirit Energy by possessing greater Spiritual Pressure.

Colors
Different spirits have different colors of reiatsu, and it does not depend on the character's race or power; instead, the color is determined by the owner’s personality.


 * Black: Ichigo Kurosaki (Final Getsuga Tenshō)


 * Black with Blue Outline: Ichigo Kurosaki (Bankai)


 * Black with Green Outline: Ulquiorra Cifer (Resurrección)


 * Black with Purple Outline: Kaname Tōsen (Hollow mask and Resurrección)


 * Black with Red Outline: Ichigo Kurosaki (Bankai and Hollow mask)


 * Blue: Grimmjow Jaegerjaquez, Coyote Starrk, Izuru Kira, Kōga Kuchiki


 * Golden-Yellow: Kenpachi Zaraki, Tier Harribel, Nnoitra Gilga, Suì-Fēng, Orihime Inoue


 * Green: Ulquiorra Cifer, Yumichika Ayasegawa, Shūhei Hisagi, Ginrei Kuchiki


 * Light Blue: Ichigo Kurosaki, Uryū Ishida, Suì-Fēng (Bankai)


 * Multicolored: Maki Ichinose


 * Pink: Yachiru Kusajishi, Mayuri Kurotsuchi, Szayel Aporro Granz, Marechiyo Ōmaeda, Kaname Tōsen, Loly Aivirrne, Hiyori Sarugaki , Zommari Rureaux , Cyan Sung-Sun


 * Orange: Hachigen Ushōda


 * Orange-Red: Yammy Llargo (Resurrección), Franceska Mila Rose


 * Red: Renji Abarai, Baraggan Louisenbairn, Sajin Komamura, Mayuri Kurotsuchi (Bankai), Momo Hinamori, Ikkaku Madarame, Kisuke Urahara, Genryūsai Shigekuni Yamamoto , Emilou Apacci , Hollow Ichigo


 * Violet: Sōsuke Aizen


 * White: Byakuya Kuchiki, Tōshirō Hitsugaya, Rangiku Matsumoto, Suì-Fēng (Shunkō), Yoruichi Shihouin (Shunkō)


 * White with Red Outline: Hollow Ichigo (Bankai, in Ichigo's inner world)

Shape
Some particular characters have a shape or manifestation of their energy whenever they release enough of it. The manifestations are one of the characters inner strength/energy.


 * Ichigo Kurosaki: Blue Spiritual energy in the shape of his Hollow mask.
 * Kenpachi Zaraki: Golden Spiritual energy in the shape of a giant menacing skull.
 * Yachiru Kusajishi: Pink Spiritual energy in shape of a cat.

Defensive use
When two spiritual beings collide, the side with weaker spiritual pressure will get hurt. (Ex: When Ichigo Kurosaki fights Kenpachi Zaraki, the captain opened up the chest area of his Shihakushō, and ordered Ichigo to cut him. When attacking with all his strength, Ichigo found Kenpachi uninjured, while his own hands were bleeding. As his sword that is highly concentrated for the purpose of killing, the spiritual pressure that Kenpachi subconsciously releases is much, much stronger). It was not until he increased his own reiatsu that he was able to cut Zaraki. With sufficient enough power, Shinigami can use their own reiatsu to harden their skin, and effectively protect themselves from attacks.

Psychological use

 * Fear: Reiatsu at its most basic level can instill fear in others when it is very high (in comparison to the one feeling it). Willpower is the simplest way to fight this method.
 * When Ichigo fought Kenpachi for the first time he felt it was impossible to win, making his reiatsu far weaker than normal. Kurosaki was able to fight Zaraki only once he was able to counter with his reiatsu.
 * When Nanao Ise stared into the eyes of Captain-Commander Yamamoto she felt it was impossible to win.


 * Stunning: High level of spiritual power can cause those of lower power to be stunned by simply being in the presence of a high level spiritual being.
 * It is not uncommon for Humans and souls alike to get the wind knocked out of them by simply being near a spiritual being with a high level of spiritual pressure.
 * Kenpachi Zaraki's spiritual pressure was so high that Hanatarō Yamada fell to his knees, Ganju Shiba could barely stand upon coming into 20 feet of him.


 * Paralysis: When a Spiritual being of high reiatsu chooses to they can paralyze an opponent just by focusing pressure through their stare.
 * Yamamoto stares directly into Lieutenant Nanao Ise's eyes paralyzing her from movement.
 * Sōsuke Aizen and Gin Ichimaru have also been shown to be able to use this ability.


 * Phantom Pain: High level of spiritual pressure can make an opponent feel as though they are being attacked though nothing is physically happening to them.
 * Captain Zaraki went after who he thought was the strongest of the intruders, Ichigo Kurosaki. As Ichigo and his group ran, he felt like there was a sword to his neck, following no matter how fast they ran.
 * Upon coming face to face with Kenpachi, Ichigo literally felt like he was just stabbed, but in reality, he simply saw just how massive Kenpachi's killing intent was.

Offensive use

 * Damage: Lieutenant Renji Abarai and Captain Tōshirō Hitsugaya released their limiters, unleashing a huge amount of spiritual pressure. Both Shawlong Kūfang and Yylfordt Granz were slightly frozen and burned respectively. During the fight with Szayel Aporro Granz, Renji once again used spiritual pressure transferred through his blade in order to injure the Espada. His reiatsu was able to cut his face since he was holding Zabimaru so close. Also, Captain Kenpachi Zaraki has consistently been shown to be able to focus his reiatsu through his sword to create powerful shockwaves, usually damaging the surrounding environment as he does so. This use only occurs when the user is releasing a large amount of energy at once or in an emotional state.


 * Killing: In high enough quantities, spiritual pressure can be lethal to others. After his second Hōgyoku-induced transformation, Sōsuke Aizen's reiatsu was so powerful that it reduced a nearby Human to ash when he approached him, as well as destroying objects thrown at him. Similarly, Coyote Starrk's reiatsu killed a massive number of Hollows, simply by being close to him.

Standard type
Most characters have this form of reiatsu, which have no other effect than those described above, along with its unique color and feeling. Most Hollows and Shinigami have this type, while every Quincy and Human always have this type. Yasutora Sado is the only human shown to have Hollow-like powers, so naturally he felt 'more at home' in Hueco Mundo, and his reiatsu feels like a Hollow despite his species; it is still a standard type.

Dual type
All Visored and Arrancar have this specific reiatsu. For Visored, they feel more like Shinigami, while Arrancar feel more like Hollows. When Ichigo's inner Hollow started to take over Orihime could sense it, becoming afraid of how heavy and dark it was. The Visored, strangely enough, also feel more like Hollows when they release their powers. Arrancar seal their Hollow abilities, meaning they become as close to their original form as can be, explaining this phenomenon.

Element type
Four characters have been shown using elemental reiatsu, even without releasing their Zanpakutō, or it being their natural Spiritual Power: Genryūsai Shigekuni Yamamoto, Rukia Kuchiki, Tōshirō Hitsugaya, and Tatsuki Arisawa. When Tōshirō was a child, he had trouble controlling his power. In his sleep, it would go out of control, affecting his grandma and causing her to shrink thanks to the sheer cold. This cold power caused others to fear him. Captain Yamamoto has used his burning spiritual pressure to heat up his sealed Zanpakutō, causing it to glow dark orange like a recently forged sword. He has also displayed a large amount of flames emanating from his body before his Shikai, which is needed for his fire based techniques. Tatsuki has shown elemental Spiritual Power when she fought Hollows using her Riser Deadly Magnum, when she arrived inside the Giant Hollow Fortress, she incorperated it around her body.