A number of action anime series are based on the "monster hunter" mold, such as D.Gray-Man, Fire Force, Demon Slayer, and Tite Kubo's hit series Bleach. In the case of Bleach, it is the job of Soul Reapers to escort the souls of the dead to the afterlife and exorcise hollows, or evil spirits.
Hollows are known for having b0ny masks and a round hole in their bodies, but what if a hollow can remove that mask and regain its old identity? Such a being is known as an arrancar, and most of Sosuke Aizen's evil minions are indeed arrancars.
10 They Are Naturally Unstable
Arrancars can exist naturally, without the aid of Sosuke Aizen's Hogyoku sphere, but they do not do very well on their own. For one thing, their spiritual pressure tends to be unstable, probably due to their hybrid nature.
Characters in Bleach have made it clear that under normal circumstances, arrancars have wonky spiritual pressure, and only Aizen's Hogyoku sphere made their pressure stronger and more stable (and thus suitable for combat).
9 They Were Rare
Hollows like this one are quite common, which is why Soul Reapers need to be armed and learn kido when they operate in the world of the living. So, it's typical to see plenty of them while on the job, but good luck finding an unmasked one.
Before Aizen came along and used that Hogyuku, it was quite rare for hollows to fully remove their skull masks, and those that did weren't necessarily more powerful as a result. In short, only Aizen's actions made arrancars something to be feared.
8 They Use Spanish Names
Villains often have a theme or a convention to them, anything from their appearance or abilities to how they are named. In the case of arrancars, Bleach author Tite Kubo chose the Spanish language, as opposed to using Japanese terms like Soul Reapers have.
He did this because to him, Spanish has a mellow and bewitching sound, and so he used that spooky and arcane sound on the arrancars and make them more distinct villains. This contrasts with the German-inspired Sternritters in later arcs.
7 They Have Facial Markings
An arrancar can be identified not only by the broken remains of their hollow mask and their distinctive hollow hole, but also some colored markings on their faces. Nearly all arrancars have estigma markings around their eyes, on their cheeks, or even on their chins.
Some arrancar have these at all times, such as Grimmjow and Ulquiorra. Others, like Halibel and Nnoitora, only show their estigma when they perform their zanpakuto release, as pictured.
6 Their Swords Are Unusual Zanpakuto
A zanpakuto is the sword of a Soul Reaper, and these swords are alive and can think for themselves. As a Soul Reaper uses them, they learn the name and personality of their sword and unlock its potential. They are partners.
Arrancars also use zanpakuto, but only on a superficial level. These swords are really just containers for the user's original hollow form and powers, and they don't seem to think for themselves. An arrancar named Edorad Leones mentioned this while fighting Ikkaku Madarame; these are mutant hollow zanpakuto, not soul-exorcising tools.
5 They Are Cursed
There is no doubt that becoming an arrancar with Aizen's help allows a hollow to regain its human intellect and get some great powers too, but that can't change the fact that hollows are forever cursed to be seen as evil.
As Nnoitora put it, there is no salvation for hollows, even if they turn into arrancars. Zommari Rureaux, meanwhile, cursed Byakuya for trying to strike him down just because of what he was. He demands to know: who gave Soul Reapers the right to slay hollows and arrancars at will?
4 They All Have Numbers
Every arrancar under Aizen's command has a unique number, and in the case of the Espadas, those numbers are tattooed onto their bodies with black ink. Starrk is #1, Grimmjow is #6, Aaroniero is #9, and so on.
Meanwhile, what about the lesser arrancar that Aizen commands, like Loly and Menoly? All of them have numbers too, as large as #77, but these numbers are tough to figure out without the help of official Bleach guidebooks. Now one may wonder just how those numbers go in Aizen's army.
3 They Wear Unique Outfits
The Soul Reapers have a distinct uniform: black robes, white fabric belt, straw sandals, white tabi socks. These uniforms are consistent, and the Captains wear white haori robes over them. But the arrancars get more creative.
They wear inverted colors, such as white outfits with black belts and socks, but the outfits don't all look the same. Ulquiorra's has coattails and a high collar, while Zommari's has a Chinese theme and Barragan looks like a Viking warlord.
2 Some Are Missing Eyes
A few arrancar don't have visible eyeballs, based on the location of their mask remains or their hollow hole. As pictured, Nnoitora has his hollow hole where his left eye would be, and Loly and Menoly each have a hollow mask eye socket where an eyeball would be.
But their eyes can re-appear, too. Findorr Calius had a mask piece that covered his eyes, until he broke off a piece and exposed an eye. Then he exposed the other one, and in the process showed off the purple estigma markings around his eyes.
1 They Form Groups Naturally
It may tempting to think that arrancars, like hollows, are solitary beings who scorn the company of others. Some might be like that, but not others. As a Vasto Lorde and then as an arrancar, Halibel Tier adopted three hollows as her sisters.
Meanwhile, a gang of unique Gillians came across Grimmjow and accepted him as their "king," and this continued into their arrancar days. Clearly, even hollows have a concept of friendship, and there was once a colony of natural arrancars in the desert of Hueco Mundo (until Nnoitora slaughtered them).