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 ( yamen), but is pronounced as the Spanish arrancar (arankaru).
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 (shinigami-ka). 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 Dick: 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 (resurekushion, Japanese for "returning blade," Spanish for "resurrection"), 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.
Here is the order of the Espada from strongest to weakest (not order of the picture below)
2.Halibel (the only female)
The Espada Group
Picture Order-Top row: Nnoitra, Barragan, Grimmjow, Aaroniero, Halibel.
Bottom row: Yammy, Stark, Ulquiorra, Szayel, Zommari.
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 (Esupāda, Japanese for "ten blades," Spanish for "sword") 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 (Numerosu, Japanese for "number holders," and Spanish for "numbers") 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 (Furashion, Japanese for "subordinate officers," Spanish for "fraction") 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 (Puribaron Esupāda, Japanese for "ten fallen blades," Spanish for "deprived sword") 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 (Ekusekiasu, Japanese for "funerary attacking force," Spanish for "funeral rites") are arrancar that are part of the execution division, apparently charged with termination of intruders and rebels.
Aizen's arrancar reside in Las Noches (Rasu Nōchesu, Spanish for "the nights," Japanese for "hollow night palace"), 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.
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 (Bara, Japanese for "hollow bullet," Spanish for "bullet") 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 (Sero, Japanese for "hollow flash," Spanish for "zero", labeled as "Doom Blast" in the Viz manga) 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 pussy 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 (guran rei sero, Japanese for "royal hollow flash," Spanish for "great king zero") and Pesshe Gatiishe and Dondochakka Bilstin's cero sincrético (sero shinkuretiko, Japanese for "united hollow flash," Spanish for "synchronized zero").
Garganta (Garuganta, Japanese for "black cavity," Spanish for "throat") 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 (Iero, Japanese for "steel skin," Spanish for "iron") 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 (Negashion, Japanese for "counter-membrane," Spanish for "negation") 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 (Kaha Negashion, Japanese for "negation of counter-membrane," Spanish for "Negation Box") 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 (Pesukisu,Japanese for "inquiry circuit," Spanish for "inquiry") is the arrancar equivalent of the shinigami ability to sense spiritual pressure.
Sonido, Japanese for "resounding revolution," Spanish for "sound") 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.