Hollows (Kaiser)

Hollow (虚 (ホロウ), Horō) are a race of creatures which are born from  who, for various reasons, do not cross over to Soul Society after their death and stay in the  for too long. They are corrupt spirits with supernatural powers which devour the souls of both living and deceased Humans. Hollows settle in, but can cross over to the Human World and Soul Society. Hollows are the opposite of Humans.

Overview
Hollow are former es (deceased Human souls) who lose their hearts to despair or regret, or they remain in the Human World for too long. Any spirit who is not guided to Soul Society by a via  may eventually turn into a Hollow.

Transformation Process
The majority of ghosts peacefully move on to the Soul Society after their deaths. However, some stay in the living world to fulfill certain goals, such as looking after a loved one, protecting a particular location, or pursuing a grudge from beyond the grave. However, with only limited abilities to interact with the living, and by definition tied to their goals, many ghosts find they are unable to cope when their loved ones move on or old enemies forget them. At this point, some will become dangerously obsessed with fulfilling those goals, even if the means to fulfill them renders the soul empty: for example, killing anyone who comes near a loved one in order to keep them from hurting that person. In doing so, the ghost warps into a Hollow and, ironically, often makes the focus of their obsession into their first victim, such as what Glaciersharp did to a woman he had great affection for. This can be prevented if a Shinigami gives the soul a Soul Burial before it turns into a Hollow.

The process by which a soul becomes a Hollow usually takes months to years to complete, reflected by the length of the soul's, which usually resides in the center of their chest, and connects to their bodies, if present. The Chain of Fate slowly corrodes over time, coinciding with the degradation of the soul's ties to the living world. The process can be accelerated under certain conditions, such as being attacked by a Hollow, giving into extreme despair, or using certain spiritual powers. When the chain completely decays, they become a Hollow when a hole opens up on their chest where the chain was attached, signifying they have lost their heart.

Tendencies
Once a soul becomes a Hollow, it is driven by an eternal and insatiable hunger to devour other souls, living or dead, to fill the void caused by its descent. While their former obsession often becomes their first target, most Hollows will eventually become mindless creatures concerned only with finding the most potent souls to devour. Stronger and more evil Hollows are often able to retain some of their intelligence in Hollow form, making them more dangerous than the average Hollow. While most Hollows are evil, or at the very least mindless, at least a few are not, as is the case with and her Hollow companions. They are at least partly capable of camaraderie and loyalty, as seen with and his companions while they were still Hollows; Grimmjow's subordinates voluntarily sacrificed parts of their bodies for the sake of Grimmjow's growth.

Appearance
All Hollows wear masks, which are formed from the hearts they had lost as Humans. This mask protects the naked instinct which is left in a being after the loss of its heart, and obscures the original identity of the Hollow. The masks of different Hollows can differ greatly in shape and form, but are always white and skull-like. The mask can be shattered, temporarily allowing the Hollow to regain its original identity, but it will regenerate after a short period once the Hollow takes over again.

Hollows have widely varying physical characteristics, rarely appearing the same. In terms of appearance, Hollows can range in appearance from furry (like mammals) to lizard-like to outright demonic. Hollows vary in size, though it tends to be fairly consistent among the various classifications of Menos. In Hueco Mundo, some Hollows are no larger than common pets. Most common Hollows are about twice the size of an adult Human, though it can vary to a degree.

It is revealed by how Hollows gain their unique appearance and individual powers. When a Hollow's heart is carved out by the hole in their chests, the lost heart becomes its mask and changes its outward appearance to what it looks like as a Hollow. The powers a Hollow wields are manifestations of its heart.

Destruction
Hollows are usually killed by splitting their mask and head in two, but most wounds which would be fatal for a Human will effectively dispatch them. When this is done by a Shinigami's Zanpakutō, the Hollow is not truly killed; its spirit is purified of the sins it committed as a Hollow. This allows the spirit within to enter the Soul Society as a Plus. In cases where a Hollow committed great sins as a mortal, its purification will summon the gates of, through which the soul is dragged to its punishment. When a Hollow is killed by a, it is destroyed, soul and all, which has potentially disastrous effects on the spiritual balance of the worlds. The effects of other spiritual powers on Hollows, such as those of or Fullbring users, are unknown, partly because such occurrences are rare.

A Hollow's spiritual power is essentially poison to Quincy, and would destroy their souls completely should it enter their bodies, with no chance of even Hollowfication to occur. It is for this reason that the Quincy sought to destroy Hollows completely, as a philosophy of preserving their own existence.

Demi-Hollow
A Demi-Hollow (半虚 (デミ・ホロウ), demi-horō; lit. "Half-Hollow") is a, an earthbound spirit who is evolving into a Hollow. It usually takes a while for the earthbound spirit to fully transform into a Hollow, but this process can be sped up by forcing the hole in their chest to open. The Demi-Hollows are held down by chains, usually to a place they consider to be their territory. They are usually only seen when a Human steps on their territory and cannot be easily sensed by Shinigami.

Menos
Though most Hollows are simply transformed Human souls, a sub-group of Hollows known as Menos (メノス, menosu; Spanish for "Minus" or "Less"), exist. Menos are conglomerations of hundreds of normal Hollows, resulting in a single composite entity of far greater strength than any normal Hollow.

Menos are created when the void within an ordinary Hollow's heart becomes so substantial Human souls are incapable of sustaining it, at which point it begins devouring fellow Hollows. These cannibal Hollows are attracted to one another, and a mass inter-devouring follows, resulting in a Gillian. Following this transformation, the Gillian can evolve twice more, first into an Adjuchas and finally into a Vasto Lorde, provided certain conditions are met. Menos evolution is not only contingent upon the Menos eating other Hollows, but also upon the Menos' ability to avoid being eaten. If another Hollow succeeds in devouring even a part of their body, evolution becomes impossible for the one who was wounded this way. Menos-class Hollows are considered so dangerous Soul Society sends only highly trained Shinigami teams to handle them. These incursions seem to be rare, however, as Menos rarely leave Hueco Mundo unless attracted by large sources of spiritual power or encouraged to by other forces. There are three categories of Menos: Gillian, Adjuchas, and Vasto Lorde.

Gillian
Gillian (最下大虚 (ギリアン), girian; Japanese for "Lowest Great Hollow"), also called Menos Grande (大虚 (メノスグランデ), menosu gurande; Spanish for "Less Big" or "Big Minus"; Japanese for "Great Hollow") are the first and weakest of all Menos. In Human terms, they would be considered foot soldiers. There are many of them, and they all look alike. In Soul Society, they are the "Menos" who are generally referred to in textbooks. Gillians are huge, but they are slow and have beast-like intellect, though this can change should one of the minds that make up their form gains dominance, granting them greater intelligence to go with their gargantuan form. Despite being numerous, encountering one outside of Hueco Mundo is rare and Shinigami can go decades without ever meeting one. When they do appear, they do so in groups and just one is capable of challenging Lieutenant-level opponents, though their power rarely poses any threat to those of Captain-level.
 * Signature Powers:, ,.
 * Evolution: Though Gillians usually have no personality to speak of, which makes them dangerous since they have no mind of their own, one of the many Hollows which comprise it might gain control over the newly formed entity, reflected in the unique mask it wears in comparison to a normal Gillian. Only these Gillian variants have the potential to evolve into Adjuchas-class Menos. The evolution is facilitated by the continued cannibalization of fellow Hollows, even other Gillians.

Adjuchas
If a Hollow can gain dominance within the form of a Gillian, beating down the wills and consciousness of the great many other Hollows that comprise its body, they can take control and then evolve further, becoming an Adjuchas (中級大虚 (アジューカス), ajūkasu; Japanese for "Intermediate Great Hollow"). They are rarer than the Gillians, due to the difficulty of trying to take control of a Gillian's form. Gillian-class Hollows appear to be subservient to them and are quick to follow their commands. An Adjuchas is forced to continue the cannibalization of other Hollows or be faced with reverting back into a Gillian as the wills of others continue to try and overwhelm them. They are thus powerful but often solitary beings, capable of taking on Captain-level opponents.
 * Signature Powers:,.
 * Evolution: Adjuchas-class Menos are much smaller in population compared to the Gillian class, due to the rarity of any one Hollow being capable of overwhelming the many other Hollows which comprise the body of a Gillian. Furthermore, the Adjuchas must continue to devour Hollows, or its mind will be absorbed by the other Hollows comprising its form, and it will revert into a Gillian. The subsequent lack of an individual will prevent the reverted Gillian from becoming an Adjuchas again. If any part of an Adjuchas is devoured, they permanently cease evolving and possibly stop regressing into a Gillian, as the Adjuchas in Grimmjow's group asked him to eat them so they would not regress.

Vasto Lorde
The third classification of Menos and the highest level of evolution. The Vasto Lorde (最上大虚 (ヴァストローデ), vasuto rōde; Japanese for "Highest Great Hollow") are extremely small Hollows, roughly the same size as humans, and are extremely rare in number. It is said that their entire number within Hueco Mundo can be counted with the fingers on one's hands. The combat capabilities of Vasto Lorde are far beyond that of the Captains of the Gotei 13, such that a gathering of only three of them forced the entire Captaincy, including the Captain-Commander to attempt to deal with them. The exact requirements for becoming a Vasto Lorde are unknown, though devouring other Hollows remains a part of the ascension process, it is known that simply eating others will not transform one into a Vasto Lorde as others had realized they're power no longer increased with the cannibalizing of Hollows beyond the 1,000 range.
 * Signature Powers: Unknown

Arrancar

 * Main article: 

An Arrancar (破面 (アランカル), arankaru; Spanish for "To Tear Off", Japanese for "Ripped Mask") is a Hollow that has removed its mask and has gained Shinigami-like powers.

Visored

 * Main article: 

The Visored (仮面の軍勢 (ヴァイザード), kamen no gunzei (vaizādo); Japanese for "Masked Army"; Viz: Vizard) is a group of Shinigami that have acquired Hollow powers.

Resucitar

 * Main article: Resucitar Alma

Isshindōtai

 * Main article: Isshindōtai

The Isshindōtai (一心同体); Japanese for "being one in body and sou") are a sub group of allow evolution. Born with a hollow merges its spiritual energy with that of another race.

Powers
Like Shinigami, Hollows have a multitude of combat skills and abilities, most of which are usually unique to specific Hollows. The more powerful Hollows, however, have access to a range of techniques of greater power or use than their own unique skills. Hollows usually acquire energy to power their abilities by devouring souls, but smaller ones can ingest energy from the atmosphere when in realms with a high concentration of spiritual energy, such as Hueco Mundo.
 * Acidic Touch: When a Hollow grabs a Human with their hands, the spot where the person was grabbed is burned as if acid were poured onto it. This occurred when Orihime was grabbed by the leg, and when 's back was wounded. These wounds seem to allow the Hollow's reiatsu to seep into the person, causing great pain to the victim. The wounds can heal if given enough time.
 *  (虚閃 (セロ), sero; Spanish for "Zero"; Japanese for "Hollow Flash") is a highly powerful and relatively swift energy blast which can be fired from various body parts, such as the mouth, tongue, hand, or fingers. Only Menos, Arrancar, and Visored have used Cero attacks, and it appears stronger entities can use it more efficiently and forcefully. With the exception of a few Cero techniques and users, Cero requires some time to be used effectively, so the enemy must be not moving, busy with something else, or too badly wounded to even simply dodge it. There exist a number of variations of Cero, which are usually unique to the one using it.
 *  (黒腔 (ガルガンタ), garuganta; Spanish for "Throat"; Japanese for "Black Cavity") is how Hollows and Arrancar move to and from Hueco Mundo. It literally tears open the dimensional fabric separating the worlds, revealing a tunnel of whirling, torrential energy which must be focused and solidified to create a discernible pathway.
 *  (超速再生, Chōsoku Saisei; lit. "Ultra-Fast Regeneration") is an ability which allows a Hollow to heal most injuries very quickly, with the exception of the destruction of the head or vital organs.
 *  (反膜 (ネガシオン), negashion; Spanish for "Negation"; Japanese for "Counter-Membrane") fields are used to rescue fellow Hollows.
 * Soul-Body Seperation: This technique allows a Hollow to forcibly extract a living spirit from his/her body. It is usually not used because Hollows tend to go after Pluses, who have no physical or living body to speak of. used this on his younger sister, Orihime, so she could see and converse with him.  used it for more sinister means, causing the young boy  to be trapped within the body of a parakeet for three months while the Hollow chased him. The soul is still attached by the Chain of Fate and can be saved, but if it is broken (in Yūichi's case), the soul can prevent the Encroachment so long as he/she is placed inside a soulless body or animal.

Trivia

 * has used a Spanish motif for Hollows and Arrancar throughout the series.
 * Many Hollow names and related terms contain double letters. The words Hollow and Arrancar, as well as many Arrancar including all Espada and Privaron Espada, have this trait.
 * Many Hollow and Arrancar have their Hollow holes in different places other than the chest.