|Average Height||Twice the height of a human, although this can vary|
|Universe of Origin||Bleach|
OverviewHollows are former Pluses (deceased Human souls) that lose their hearts to despair or remain in the real world for too long. Any spirit that is not guided to the Soul Society by a Shinigami via Konsō may eventually descend into a Hollow.
The majority of ghosts peacefully move on to the Other World after their deaths. Some, however, stay in the living world to fulfill certain goals, such as looking after a loved one, protecting a particular location, or pursuing a grudge from beyond the grave. However, with only limited abilities to interact with the living, and by definition tied to their goals, many ghosts find they are unable to cope when their loved ones move on or old enemies forget them. At this point, some will become dangerously obsessed with fulfilling those goals, even if the means to fulfill them renders the soul empty: for example, killing anyone who comes near a loved one, in order to keep them from hurting that person. In doing so, the ghost warps into a Hollow and, ironically, often makes the focus of their obsession into their first victim. This can be prevented if a Shinigami gives the soul a Soul Burial before it descends into a Hollow.
The process by which a soul becomes a Hollow usually takes months to years to complete, reflected by the length of the soul's Chain of Fate, which resides in the center of their chest. The Chain of Fate slowly corrodes over time, coinciding with the degradation of the soul's ties to the living world. The process can be accelerated under certain conditions, such as being attacked by a Hollow, giving into extreme despair or through the use of certain spiritual powers. When the chain completely decays, they become a Hollow when a hole opens up on their chest, where the chain was attached, signifying that they have lost their heart. Once a soul becomes a Hollow, it is driven by an eternal and insatiable hunger to devour other souls, living or dead, to fill the void caused by its descent. While their former obsession often becomes their first target, most Hollows will eventually become mindless creatures concerned only with finding the most potent souls to devour. Stronger and more evil Hollows are often able to retain some of their intelligence in Hollow form, making them more dangerous than the average Hollow. While most Hollows are evil, or at the very least mindless, at least a few are not. They are also at least partly capable of camaraderie and loyalty.
All Hollows wear masks, which are formed from the hearts that they had lost as Humans. This mask protects the naked instinct that is left in a being after the loss of its heart, and to obscure the original identity of the Hollow. The masks of different Hollows can differ greatly in shape and form, but are always white and skull-like. The mask can be shattered, temporarily allowing the Hollow to regain its original identity, but it will regenerate after a short period once the Hollow takes over again.
Hollows have widely varying physical characteristics, and few of them ever appear the same. In terms of appearance, Hollows can range in appearance from furry (like mammals) through lizard-like to outright demonic. Hollows also vary in size, though it tends to be fairly consistent amongst the various classifications of Menos. In Hueco Mundo, some Hollows are no larger than common pets. Most common Hollows are about twice the size of an adult Human, though it can vary to a degree.
The reason Hollows gain their unique appearance and individual powers is when a Hollow's heart is carved out by the hole in their chests, the lost heart becomes its mask, and changes its outward appearance to what it looks like as a Hollow. The powers a Hollow wields are also manifestations of its heart.
Hollows are usually killed by splitting their mask and head in two, but most wounds that would be fatal for a Human will effectively dispatch them. When this is done by a Shinigami's Zanpakutō, the Hollow is not truly killed; its spirit is purified of the sins it committed as a Hollow. This allows the spirit within to enter the Soul Society as a Plus. In cases where a Hollow committed great sins as a mortal, its purification will summon the gates of Hell, through which the soul is dragged to its punishment. When a Hollow is killed by a Quincy, however, it is destroyed, soul and all, which has potentially disastrous effects on the spiritual balance of the worlds. The effects of other spiritual powers on Hollows, such as those of Orihime Inoue or Fullbring users, are unknown, partly due to the fact that such occurrences are rare.
- Soul-Body Separation: This technique allows a Hollow to forcibly extract a living spirit from his/her body. It is usually not used because Hollows tend to go after Pluses, who have no physical or living body to speak of. The soul is still attached by the Chain of Fate and can be saved, but if it is broken then the soul can prevent the Encroachment so long as he/she is placed inside a soulless body or animal.
- Acidic Touch: Many Hollows, have displayed this ability, although this is implied that all Hollows possess this power. When a Hollow grabs a Human with their hands, the spot where the person was grabbed is shown to get burned as if acid were poured onto it. These wounds seem to allow the Hollow's reiatsu to seep into the person, causing great pain to the victim. The wounds can heal if given enough time though, and it is unknown if this ability works on Super Saiyans or other spiritually powerful beings.
- Cero (虚閃 (セロ), sero; Spanish for "Zero", Japanese for "Hollow Flash", 'Doom Blast' in the Viz translation) is a highly powerful and relatively swift energy blast that can be fired from various body parts, such as mouth, tongue, hand or fingers. Only Menos, Arrancar, and Visored have so far been shown to use Cero attacks, and it appears that stronger entities can use it more efficiently and forcefully. Cero also requires some time to be used effectively, so the enemy must be either not moving or busy with something else, or too badly wounded to even simply dodge it, with the exception of a few Cero techniques and users. Additionally, there exists quite a number of variations of Cero, which are usually unique to the Arrancar using it.
- Garganta (黒腔 (ガルガンタ), garuganta; Spanish for "Throat", Japanese for "Black Cavity") is how Hollows and 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.
- Negación (反膜 (ネガシオン), negashion; Spanish for "Negation", Japanese for "Counter-Membrane") fields are used to rescue fellow Hollows. Only the Gillian-class Menos have shown the ability to use it. Espada have a special cube-shaped device called Caja Negación (反膜の匪 (カハ・ネガシオン), kaha negashion; Spanish for "Negation Box", Japanese for "Anti-Membrane of Negation") (Caja de Negación in the English dub) meant to simulate Negación fields, which are used to trap and punish their subordinates if necessary. 
- High-Speed Regeneration (超速再生, Chōsoku Saisei; lit. "Ultra-Fast Regeneration") is the ability that allows a Hollow to heal most injuries very quickly, with the exception of the destruction of the head or vital organs.