Números

The are the combat specialists in Sōsuke Aizen's army of Arrancar.

Overview
The Números 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 the Números is thought to be superior to all other arrancar, except for the Espada (current and former). The strongest Números are chosen by the Espada to become their Fracción. Most of Grimmjow's Fracción have high numbers, implying that they were among the first Números created. Wonderweiss Margera is apparently one of the youngest and the youngest Números to appear in the manga.

Fracción
The are a subsection of the Números that directly serve a specific Espada. The number of fracción for any given Espada varies: Stark and Jiruga would seem to have just one, while Granz has at least a dozen. There are a few Espada that apparently prefer to fight alone, such as Yammy, Zommari, Aaroniero, and Ulquiorra, and chose not to have any fracción under their command. The fracción are all fiercely loyal to their respective Espada masters (due the the latter's impressive amount of power), perhaps even more so than they are to Aizen, and will diligently follow any order their masters give them.

Fracción Relationships
Lilinette's relationship with Stark is unique amongst the Espada and their Fracción, appearing more comical and light-hearted. She does not address him with the -sama suffix (a Japanese title similar to Lord or Master), like the other Fracción do for their respective Espada, and simply calls him "Stark". She acts more like a younger sibling than a servant, though Stark does not seem to mind. Despite her usual attitude towards him, Lilinette is very confident in Stark's abilities, actually warning Ukitake that it would be better to attack him two-on-one.

Barragan's Fracción are fiercely loyal to him--possibly more so than they are to Aizen--and willingly obey his every command. His Fraccion treat him like a king (referring to him as "his majesty"), with Pō going even further and seeing Barragan as a "god". Much like Barragan himself, they are all very arrogant and boastful. Barragan was angered when four of his underlings were killed, but this was probably more out of pride than actual concern.

Halibel's Fracción respect her and take everything she says seriously, as they should given an Espada's immense amount of power. They may even be somewhat intimidated by her given their facial reactions when she told them that it's "understandable to be afraid" of an Espada's Resurrección form. They themselves appear to have a strained, yet somewhat comical, relationship with one another. Despite this, they work quite well together, and are capable of using powerful combination attacks. Unlike most of the other Espada, Halibel actually cares about her subordinates and angrily assaulted Captain Tōshirō Hitsugaya when they were defeated by captain Shigekuni Yamamoto-Genryūsai.

Nnoitra's lone Fracción, Tesla, idolizes him and remains loyal to the end, despite Nnoitra's occasional mistreatment of him. Nnoitra himself cared for Tesla's well being enough to warn him of Kenpachi Zaraki's power and told him to run (though he insulted him while doing so and did not show any grief over his death). Tesla did not seem to have his admiration for Nnoitra while the latter was the eighth Espada; it is unclear what changed his mind.

Grimmjow's Fracción are loyal and obedient, but disregard their comrade, Di Roy, considering him the weakest of Grimmjow's Five Fracción, and reluctantly accepting his 'assistance' during Grimmjow's Assault on Karakura. Edrad Liones scornfully calls him 'an arrancar in name only'. All of them are quite cocky, much like Grimmjow, and most appear rude and unwilling to even bother learning their opponents' names (with the exception of Shawlong).

Szayel's Fracción are more like cloned drones than henchmen and he shows little to no concern over them, even going so far as to cannibalize them in order to replenish his strength and regenerate his wounds, as seen during his fight with Renji Abarai and Uryū Ishida. Szayel apparently treats them as mindless lab-rats whose only real purpose is to defend him from his enemies and for his experiments. Amongst the Espada, Szayel has by far the most Fracción.