Hollow (Bleach)

Hollows (虚（ホロウ）) are a fictional race of malignant ghosts in the anime and manga series Bleach created by Tite Kubo. They are corrupt spirits that devour the souls of both living and deceased humans. Hollows are the principal antagonists during the first part of the series and remain a primary threat beyond that point. Hollows settle in Hueco Mundo (Spanish, lit. hollow world), but can cross over to the human world and Soul Society to devour souls. Tite Kubo mainly uses a Spanish motif for hollows and arrancar.

Overview
Hollows are former pluses (deceased souls) that lose their hearts to despair or remain in the real world for too long. Any spirit that is not guided to Soul Society by a Soul Reaper may eventually descend into a hollow. The process by which a soul becomes a hollow usually takes months (if not longer), reflected by the length of the soul's Chain of Destiny (因果の鎖), which resides in the center of their chest. The Chain of Destiny slowly corrodes over time, reflecting the degradation of the soul's ties to the living world. The process can be accelerated under certain conditions, such as being attacked by another hollow or through the use of certain spiritual powers. When the chain completely decays, the soul is warped into a unique and monstrous form with a vaguely skeletal mask and a large hole where their chain was once connected.

In Bleach, the majority of ghosts peacefully move on to Soul Society after their deaths. Some, however, 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 Orihime's brother, Sora, does.

Once a soul becomes a hollow, it is driven to devour other souls, living or dead, to fill the void caused by its descent. While their former obsession often becomes their first target, many hollows will eventually become mindless creatures concerned only with finding the most potent souls to devour. Stronger willed or more evil hollows are often able to retain some or all 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 Nel Tu and her hollow companions.

The most distinctive feature of a hollow, their mask, is formed to protect the naked instinct that is left in a being after the loss of its heart, and in some ways is the tangible form of the hollow's madness. The masks of different hollows can differ greatly in shape and form, but they are always white and skull-like. The masks also obscure the original identity of the hollows. 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 and powers, and few hollows ever appear the same (the few that do are often clones). In terms of appearance, hollows can range from furry (like mammals) or lizard-like in appearance to outright demonic. A hollow's abilities are often determined by their power. Weaker (and by definition less intelligent) hollows usually only attack in a melee style, whereas stronger hollows have a wide array of abilities with which to kill their quarry. Hollows also vary in size, though it tends to be fairly consistent amongst the various classifications of hollows. 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. Huge hollows, aptly named for their size, are as large as two-story buildings. Finally, gillian-class menos are even larger than the huge hollows, standing as tall as a common skyscraper.

Hollows are usually killed by splitting their mask and head in two, but most fatal wounds will effectively dispatch them. When this is done by a Soul Reaper'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 Soul Society as a plus. In cases where a hollow committed great sins as a mortal, its purification will summon the gates of Hell, which drag the soul to its punishment. When a hollow is killed by a Quincy, however, it is destroyed, soul and all, which has potentially disastrous effects on the spiritual balance of the worlds. The series doesn't address the effects of other spiritual powers on hollows, such as those of Orihime Inoue or Yasutora Sado, but such occurrences are rare.

Menos
Though most hollows are simply transformed human souls, a sub-group of hollows known as menos (メノス), exist. Menos are conglomerations of many normal hollows (from hundreds to thousands, depending on the type), resulting in a single composite entity of far greater strength than the hollows that spawned it. Menos-class hollows are considered so dangerous that Soul Society sends only highly trained Soul Reaper 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.

Menos are created when the void within an ordinary hollow's heart becomes so substantial that 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 a part of their body, evolution becomes impossible.

Gillian (最下大虚（ギリアン）) are the weakest class of menos and the first stage of menos evolution. They are giant in comparison to other hollows, dwarfing even the largest standard hollows by at least the size of a two-story building, but lack agility and intelligence. While a gillian-class menos is quite powerful, they are still much weaker than a Soul Reaper lieutenant. According to Tōshirō Hitsugaya, they are comparable to "foot-soldiers", reflected in their uniform appearance. In Soul Society, gillians are known as Menos Grande and are shown in textbooks discussing menos. Menos Grande literally means "big minus" in Spanish ("less big" is also a possible translation) or "less". Similarly, the kanji for menos grande means 'big emptiness'.

Though gillians usually have no personality to speak of, one of the many hollows that comprise it may retain control over the new 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, resulting in a unique but still massive form before they completely become adjuchas.

Adjuchas (中級大虚（アジューカス）) are the medium class of menos in terms of power, and the second stage in the menos evolution. Adjuchas can vary radically in appearance, from bulky humanoids to the panther-like form of Grimmjow Jeagerjaques. Unlike the gillians, they are roughly human-sized. They are also much smarter than the gillians and have the power to match. It is likely they could fight evenly with at least a Soul Reaper lieutenant. They watch over the many gillian-class menos. In the anime, the adjuchas put in charge by Aizen can control the gillians, though it's unclear if this is an innate ability or something granted by their status.

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 that comprise the body of a gillian. Furthermore, the adjuchas must continue to devour hollows, or its mind will be absorbed by the hollows comprising its form and it will revert back into a gillian. The subsequent lack of an individual will also preclude the reverted gillian from becoming an adjuchas again.

Vasto lorde (最上大虚（ヴァストローデ）) are the most powerful class of menos, and the final stage in the menos evolutionary line. They appear almost completely humanoid, and each one is stronger than an average Soul Reaper captain; Tōshirō claims that ten of them under Sōsuke Aizen's control would be enough to defeat all of Soul Society. It seems that Aizen has important plans with them, but the details haven't been revealed.

Vasto lorde are the least common form of menos, but the exact population is unknown. They are believed to reside within the very depths of Hueco Mundo. Apart from the need to cannibalize even more hollows, any special requirements for the creation of a vasto lorde are unknown.

Arrancar
An arrancar is a hollow that has removed its mask and gained Soul Reaper powers. The name arrancar is a Spanish verb meaning "to remove" or "to rip off," a reference to an arrancar's removal of its hollow mask. In the manga, arrancar is written using a kanji spelling meaning torn mask (破面), but is pronounced as the Spanish arrancar (アランカル).

Few hollows have the potential to remove their masks normally, and even if they manage it the change is not significant. Sōsuke Aizen is able to artificially create arrancar with the Hōgyoku, which also unlocks much more of their potential than a natural transformation would. The process of turning a hollow into an arrancar is called soulreaperification (死神化). Arrancar differ from ordinary hollows in two ways: their hollow holes are often moved, and only a small fragment of their masks remain. When hollows become arrancar, the chances of them retaining a humanoid form increase with their intelligence; only vasto lorde-class arrancar will definitely assume a humanoid form.

If powerful enough, an arrancar can seal its excess power into the form of a zanpakutō. This weapon is their original hollow powers, which can be called upon when necessary, as opposed to the living spirit of a Soul Reaper's zanpakutō. Their zanpakutō also differ in that they need not take the form of a sword: for example, Cirucci Thunderwitch's weapon takes the form of what is essentially a giant yo-yo. When an arrancar releases their zanpakutō, a process called resurrección (帰刃（レスレクシオン）), part of their original hollow form is restored, giving them access to their original abilities. While arrancar do not appear to have a second release, the act of releasing their zanpakutō exponentially increases their power, similar to the power boost afforded by a Soul Reaper's bankai.

Those arrancar under Aizen's command also have a standard theme for their clothing. Their uniforms consist of a white jacket, black sash, white hakama, and black socks with white sandals; in essence, the uniforms are basically inverted Soul Reaper uniforms.

According to Tite Kubo, many of the arrancar are named after real life architects and designers.

Arrancar ranks
The arrancar under Aizen's command are arranged into various ranks based on their strength. Not all of the existing arrancar are under Aizen's command, mostly through lack of interest on Aizen's part.

The Espada (十刃（エスパーダ）) are the top-ranked arrancar in Aizen's army. The Espada at the time of the group's introduction consists of nine males and one female. Each Espada member is chosen for their superior combat ability and then assigned a number from 1 to 10 that indicates their rank and relative power level, which is tattooed somewhere on their body (Grimmjow's is on his lower back, for instance). The Espada are given control over the Números and are regarded as the strongest arrancar in existence. Similar to the power gap between captains and lieutenants in the Gotei 13, the strength of the Espada far surpasses that of the average Número. As Aaroniero Arruruerie notes, all of the Espada except him were at least adjuchas-class menos before becoming arrancar.

The Números (数字持ち（ヌメロス）) are the combat specialists. They are assigned a two digit number at birth from 11 to 99 to indicate their age (Número 11 is the oldest, Número 99 is the youngest). The basic Número uniform consists of a white-collared jacket and robes held with a black sash. However, the uniform is customizable, giving each Número a sense of individuality. The fighting ability of Números is thought to be superior to all other arrancar, except for the Espada (current and former).

The Fracción (従属官（フラシオン）) are a subsection of the Números that directly serve a specific Espada. The number of Fracción for any given Espada varies: Stark and Nnoitra Jiruga would seem to have just one, while Szayel Aporro Granz has at least a dozen.

The Privaron Espada (十刃落ち（プリバロン・エスパーダ）) are former Espada who have officially lost their rank and are assigned a three-digit number. Being former Espada, they are far stronger than the normal Números. They reside in Tres Cifras, which translates literally from Spanish as "three digits". As mentioned by Dordonii, these former "naturally created" Espada were rendered obsolete after Aizen began artificially creating arrancar to meet his own standards.

The Exequias (葬討部隊（エクセキアス）) are arrancar that are part of the execution division, apparently charged with termination of intruders and rebels.

Las Noches
Aizen's arrancar reside in Las Noches (虚夜宮（ラス・ノーチェス）), a massive fortress which can be seen for miles in Hueco Mundo. It consists of a main building with a domed center surrounded by several large towers and smaller buildings. Atop the dome are six smaller towers, which seem to contain areas such as Aizen's throne room and the Espada meeting hall. Like everything else in Hueco Mundo, every building is colored white.

Las Noches is easily the largest building structure in the Bleach universe, appearing as large as (if not larger than) Seireitei in Soul Society. Due to its immense size, Ichigo Kurosaki once commented that it could be an illusion as he, Chad, and Uryū Ishida did not seem to make any progress getting closer to it, despite running until they were exhausted. Also, according to the arrancar Nel Tu, it takes about three days to move from one spot to a gate.

The inside of Las Noches' domes simulate the living world and Soul Society's blue sky, which Aaroniero Arruruerie claims is so the light of the sky will help Aizen observe anywhere he wishes. However, since Aaroniero must stay out of the sunlight to use his abilities, Rukia Kuchiki speculates this is a lie. The position of the halls within the palace can also be adjusted, allowing the one operating them to direct the movements of intruders.

Powers
Like Soul Reapers, 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 similar techniques of greater power or use than their own unique skills. Hollows usually acquire energy to power their abilities by devouring souls, but can also ingest energy from the atmosphere when in realms with high concentration of spiritual energy, such as Hueco Mundo.
 * Bala (虚弾（バラ）) is an arrancar alternative to the cero. The technique hardens the user's spiritual pressure and fires like a bullet. Though weaker than a cero blast, it moves twenty times faster and can be fired at a much higher rate.
 * Cero (虚閃（セロ）) are high-powered energy blasts that can be fired from various body parts, such as the mouth, tongue, hand or fingers. Only menos, arrancar, and vizard have so far been shown to use cero attacks, and it appears that stronger entities can use it more efficiently. Various arrancar and hollow characters display variants of the technique, such as the Espada-exclusive gran rey cero (王虚の閃光（グラン・レイ・セロ）) and Pesshe Gatiishe and Dondochakka Bilstin's cero sincrético (融合虚閃（セロ・シンクレティコ）).
 * Garganta (黒腔（ガルガンタ）) is how arrancar move to and from Hueco Mundo. It literally tears open the dimensional fabric separating the worlds, revealing a tunnel of whirling, torrential energy that must be focused and solidified to create a discernible pathway. Kaname Tōsen and Kisuke Urahara have also demonstrated the ability to use garganta; Mayuri Kurotsuchi explains that Soul Society cannot do this because they haven't researched the technique.
 * Hierro (鋼皮（イエロ）) refers to the hardened skin of the arrancar, which is a result of their compressed spiritual power. While their skin is strong enough to block even released zanpakutō bare-handed, it is by no means impenetrable. Stronger arrancar have proportionally stronger skin.
 * Negación (反膜（ネガシオン）) fields are used to rescue fellow hollows. Only the gillian-class menos have shown the ability to use it. Negación fields surround a target in a square beam of light that isolates the target from the dimension they are currently in, making it impossible to harm them. The field then pulls the target towards the menos that created the field. Espada have a special cube-shaped device called Caja Negación (反膜の匪（カハ・ネガシオン）) meant to simulate negación fields, which are used to punish their subordinates if necessary. The cube, when used on a subject, traps them in an alternate dimension from which there is no escape; however, this assumes it's being used as intended. More powerful arrancar, namely the Espada themselves, can escape given enough time.
 * Pesquisa (探査回路（ペスキス）) is the arrancar equivalent of the shinigami ability to sense spiritual pressure.
 * Sonido (響転（ソニード）) is the arrancar equivalent of the Soul Reapers' flash steps and the Quincy hirenkyaku; it allows the user to travel at incredibly high speeds for short distances. Use of sonido is punctuated by a brief static sound, in contrast to the "swish" sound used for flash steps.