Espada

The are the top-ranked Arrancar in Sōsuke Aizen's army of Hollow-Shinigami hybrids, are the most powerful Hollows under Aizen's command, and are the main rivals of the Gotei 13.

Outline
Those among the Arrancar that excel in killing power are chosen and favored according to their strength, they are assigned a number from one to ten. Those chosen ten are called the Espada. They have their given number carved into their very flesh. Their authority dominates those numbered eleven and above. The strength of the Espada is on a completely different level than that of the Números.

At any given time, the Espada has a nominal composition of ten members, all hand-picked and ranked by Aizen himself. Along with Aizen, Gin Ichimaru, and Kaname Tōsen, the Espada as a group possess comparable strength to Soul Society's Gotei 13 Shinigami captains.

At the time of the group's introduction, the Espada 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 (1 presumably being the strongest) that indicates their rank and relative power level, which is tattooed somewhere on their body. For instance, Grimmjow Jaegerjaquez's is located on the right side of his lower back and Coyote Starrk's is on the back of his left hand.

The Espada are given free control over the Números and may choose as many of them as they like to become their Fracción. 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. Aizen himself is confident enough of his Espada's abilities to send them out on potentially hazardous missions, such as gathering information in the real world, fighting Shinigami captains inside Las Noches and Karakura Town by themselves, and searching for the Vasto Lorde.

Being Aizen's most direct subordinates (not counting Gin Ichimaru and Kaname Tōsen), the Espada are privy to several of Aizen's plans and most intimate secrets, such as his goals of destroying Karakura Town and creating the King's Key and the location of the Hōgyoku within Las Noches. Aizen's respect for the Espada's abilities is reflected on his manner of addressing them, often referring to them as "my dear Espada" and sitting at the head of the same table with them, while discussing the events around Hueco Mundo. According to Dordonii, Aizen treats them as tools to do his bidding, but nonetheless, he wanted to take back his position as an Espada to once again be close to Aizen. In accordance with this, Aizen is not at all distressed over the deaths of the Espada and calmly congratulates the intruders in Las Noches for their victories against the Espada as he leaves for Karakura Town.

Their immense amount of power and leadership status among the Arrancar also grants each Espada the authority to exert command over Aizen's other forces within Las Noches: the Números, the Exequias, and their own Fracción. There seems to be a sort of hierarchy among the Espada; a higher-ranked member apparently can give orders to lower-ranked members. This is demonstrated when Aizen orders Ulquiorra Cifer to kidnap Orihime Inoue; the Arrancar led by Ulquiorra included Luppi (the then-sixth Espada), Yammy Riyalgo (Arrancar 10/ Cero Espada), Grimmjow Jaegerjaquez, and Wonderweiss Margera (unassigned). Various missions usually involve one or more Espada operating together, with the most senior member exercising command over the others; typical, non-combat missions, such as searching for the Vasto Lorde and gathering pre-invasion data in the Human world, include a senior Espada and a lower-ranked one being sent out in pairs. While the lower-ranked members usually have little restraint in taking their own initiative (thus exceeding their orders), higher-ranked members usually stick to Aizen's commands, and are often the first to bail the others out of trouble, because in Nelliel Tu Odelschwanck's own words, they wish to, "prevent the Espada from losing one of their own." However, Aizen's attitude toward the offending Espada members seem to be one of leniency, officially forgiving them (though not without severe sanctions) on the grounds that they are merely advancing his own wishes.

Aside from regularly appearing in Aizen's throne room and the debriefing room, the Espada are known to have their own quarters within Las Noches; those that have been seen appear to have been modified to suit the specific Espada's taste. Szayel Aporro Granz, for instance, possesses a large building that he refers to as his "palace," complete with a hidden, indestructible laboratory and a changing room; Zommari Leroux has been shown on one occasion to await orders inside a meditation room; Coyote Starrk's room is designed along the lines of a lounging chamber and Aaroniero Arruruerie's tower, accessed via a hanging bridge, effectively keeps out sunlight and contains nooks and crannies for hiding cushions and other implements whose purpose is to make his shape-shifting abilities more convincing.

According to Ulquiorra, any Espada ranked 4th or higher are not allowed to release their Zanpakutō within Aizen's palace, as their Resurrección's released powers are powerful enough to destroy the majority of Las Noches.

Most recently, Yammy Riyalgo stated that the Espada are not assigned numbers from 1 to 10, but rather, 0 to 9.

History
The creation of the Espada has long been one of Aizen's most important preoccupations. While it is not specified when the Espada were first brought together as a group, the original Espada were already in existence sometime before Aizen's defection from the Soul Society and acquisition of the Hōgyoku. Since then, the composition of the Espada has changed, both in membership and position.

At some point in the past Nnoitra Jiruga was the 8th Espada with Nelliel as the 3rd Espada and Szayel Aporro Granz was not a member at all. During this time Aizen frequently sent the Espada out to search for the Vasto Lorde-class Menos.

Before his death, Aaroniero Arruruerie was the sole member of the current Espada who was also part of the first-generation Espada. He was also the only Arrancar from Gillian-class Menos stock to attain a position among the Espada.

Former Espada
These are former Espada that did not become a part of the Privaron Espada because of certain circumstances.

Demotion
An Espada may be demoted from the group either when they lose strength or cease to be useful to Aizen, such as Grimmjow Jaegerjaquez after his left arm was cut off by Kaname Tōsen. In most cases, they will be demoted to the, who are former Espada that have officially lost their rank and are assigned a three-digit number.

Privaron Espada
The Privaron Espada 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.

Espada exclusive Powers & Techniques

 * is a variant of the Gillian-exclusive ability Negación used to punish Arrancar subordinates by trapping them eternally in an alternate dimension. However, should the Caja Negación be used on an Espada, the Espada will eventually break out of the alternate dimension (usually within a few hours), due to their large amount of Reiatsu.


 * is a particular, very strong Cero. To perform this potent variation of the Cero, the Arrancar first draws blood from the Cero-generating appendage using his or her Zanpakutō, then charges the Cero while mixing the blood with it. The result is a Cero with a much greater attack power and speed, as well as a change of color unique to the Espada. This attack was first used by Grimmjow Jaegerjaquez in order to incite Ichigo into donning his Hollow mask. Grimmjow refers to it as, "the ultimate Cero". According to Ulquiorra, it is forbidden for any of the Espada to perform Gran Ray Cero within Las Noches, as it would destroy most of the building. Grimmjow is, to date, the only Arrancar that has ever used Gran Rey Cero and Caja Negación on-screen.


 * 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.

Trivia

 * It is unknown whether the aspects of death correspond to the Espada by rank or by the characteristics of the member.
 * While he is not an Espada, Wonderweiss Margera is classified with Espada-level spiritual energy by Soul Society.

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