Arrancar Ranks

Espada

Main article: Espada

The Espada are the top-ranked Arrancar in Aizen's army, and the primary antagonists in the later half of the series. 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 0 to 9 (with 0 being the strongest, while 9 being the weakest) that indicates their rank and relative power level, which is tattooed somewhere on their body (Grimmjow's is on his lower back, for instance). Each Espada embodies an aspect of death, which ties into their personalities, beliefs and powers. 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, speed, intelligence, and power 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. Nelliel Tu Odelschwanck was formerly the 3rd Espada before she was tricked and exiled by Nnoitra.
Privaron Espada

Main article: 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 normal Números. They reside in the part of Las Noches called Tres Cifras (三桁の巣 (トレス・シフラス) Toresu Shifurasu Spanish for "3 Digits" Japanese for "Nest of 3 Digits" ) As mentioned by Dordonii Alessandro Del Socacchio, these former "naturally-created" Espada were rendered obsolete after Aizen began artificially creating Arrancar to meet his own standards. It is also noted that Aaroniero Arruruerie was one of the original Espada, but his original number was not mentioned since it is possible he was demoted to a lower number in accordance to the arrival of more powerful Espada.
Números

Main article: Números

These Arrancar are the combat specialists. They are assigned a two digit number at birth from 11 to 99 to indicate their age (Número 11 being the oldest, while 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).
Fracción

Main article: Fracción

The Fracción are a subsection of the Números that directly serve a specific Espada. The number of Fracción for any given Espada varies: Nnoitra Jiruga seems to have just one, while Szayel Aporro Granz has at least a dozen. There are a few Espada that apparently prefer to fight alone, such as Coyote Starrk, Yammy Riyalgo, Zommari Leroux, Ulquiorra Cifer and Aaroniero Arruruerie, who seem to have chosen not to have any Fracción under their command.
Exequias

Main article: Exequias

The Exequias are Arrancar that are part of the execution division, apparently charged with termination of intruders and rebels. They are the equivalent of Soul Society's Onmitsukidō. Their captain is the bull-headed Rudobōn, who can spawn a seemingly infinite amount of the soldiers that form this group using his Zanpakutō.


~Wikipedia.~