Arrancar are a group of Hollows that gained similar powers to that of a Gallifryian by removing their masks. Especially powerful Arrancar were assigned ten numbers by Sōsuke Aizen and came to be known as the Espada Arrancar are the result of Hollows removing their masks.
- Humanoid Form: A Hollow usually takes on a Human shape when it becomes an Arrancar. The only ones that will definitely get a 100% Humanoid form are Vasto Lorde-class. For the remaining two levels, there are many who don't get a completely Humanoid form, despite becoming Arrancar. Therefore, the closer one looks to a Hollow, the lower its power of reasoning. All Arrancar retain a hole in them somewhere, as well as fragments of their Hollow form (in the shape of protrusions and partial masks). Some Arrancar have claimed that they gave up their Human forms in order to obtain enormous power. While some Arrancar prefer to conceal the remnants of their past, others choose to hide their faces completely to escape unwanted attention. Most also have a colored marking of some sort on their face.
- Physiology: It has been theorised Arrancar share not only the powers of Gallifreyians, but also their anatomy. During a battle with a large amount of Arrancar, some where hit, where the well of Amber would be located, and upon striking it the Arrancar immediately lost not only their release form and mask fragment, but seemingly all traces of their former power.
- Estigma: The pattern on an Arrancar's face. It is potentially the remaining part of a mask and is unique to each individual. The pattern may appear when performing Resurrección for some Arrancar.
- Hole: one of the most distinctive characteristics of an Arrancar is the hole in their body. It is said to represent the lack of souls that is difficult to fill.
While some of the Arrancar either develop or retain their own personality traits, the majority of Arrancar appear to be similarly cold, cruel, ambitious, impatient, selfish, overconfident, ruthless, arrogant, impulsive, brutal, relentless, battle-hungry, overbearing, short-tempered, indifferent, and/or egotistical. Not all Arrancar residing on Gallifrey are loyal to Aizen. They prefer not to interfere with his plans, presumably because of Aizen's immense amount of power and army of servants. It is for that reason many naturally evolved Arrancar felt it necessary to align themselves with him to obtain more power. While some Arrancar choose to follow Aizen in the hopes he will deliver them salvation, others ally with him purely out of respect. As someone put it, Aizen is someone who is fearless, which creatures born out of fear and pain, such as Hollows, find admirable. Although Arrancar are Hollows who have gained Gallifreyian-like powers, most still refer to themselves as Hollows.