Hollow

Hollows (虚 (ホロウ), Horō) are a race of creatures which are born from Human souls who, for various reasons, do not cross over to the Holy Dimension after their death and stay in Dens for too long. They are corrupt spirits with supernatural powers which devour the souls of both living and deceased Humans. Hollows settle in Hueco Mundo, but can cross over to the Dens and Soul Society. Hollows are the opposite of Humans.

Description
Hollow are former Pluses (deceased Human souls) who lose their hearts to despair or regret, or they remain in the Human World for too long. Any spirit who is not guided to Soul Society by a Shinigami via Konsō may eventually turn into a Hollow.

Transformation
The majority of ghosts peacefully move on to the Soul Society after their death. However, some 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

Appearance
All Hollows wear masks, which are formed from the hearts they had lost as Humans. This mask protects the naked instinct which is left in a being after the loss of its heart, and obscures 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, rarely appearing the same. In terms of appearance, Hollows can range in appearance from furry (like mammals) to lizard-like to outright demonic. Hollows vary in size, though it tends to be fairly consistent among 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.

Some Hollows, like White, are artificially created with the same material as Asauchi. These Hollows have the ability to enter a Shinigami's soul and fuse with their Shinigami powers, forming a new Zanpakutō spirit with the abilities of both a Shinigami and a Hollow.

Destruction
Hollows are usually killed by splitting their mask and head in two, but most wounds which 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, it is destroyed, soul and all, which has potentially disastrous effects on the spiritual balance of the worlds.

Demi-Hollow
A Demi-Hollow (半虚 (デミ・ホロウ), demi-horō; lit. "Half-Hollow") is a Jibakurei, an earthbound spirit who is evolving into a Hollow. It usually takes a while for the earthbound spirit to fully transform into a Hollow, but this process can be sped up by forcing the hole in their chest to open. The Demi-Hollows are held down by chains, usually to a place they consider to be their territory. They are usually only seen when a Human steps on their territory and cannot be easily sensed by Shinigami.

Gillian
Gillian (最下大虚 (ギリアン), girian; Japanese for "Lowest Great Hollow"), also called Menos Grande (大虚 (メノスグランデ), menosu gurande; Spanish for "Less Big" or "Big Minus", Japanese for "Great Hollow") are the first and weakest of all Menos. In Human terms, they would be considered foot soldiers. There are many of them, and they all look alike. In Soul Society, they are the "Menos" who are generally referred to in textbooks. Gillians are huge, but they are slow and have beast-like intellect. Any captain-level Shinigami can destroy them with ease.

Adjuchas
Adjuchas (中級大虚 (アジューカス), ajūkasu; Japanese for "Intermediate Great Hollow") are the second classification of Menos. They are smaller than Gillians and far fewer in number. They are much smarter and stronger than Gillians, and are often the ones who lead Gillians into battle.

Vasto Lorde
Vasto Lorde (最上大虚 (ヴァストローデ), vasuto rōde; Japanese for "Highest Great Hollow") are the third classification of Menos and the highest level of evolution. They are extremely rare in number, and it is said that their entire number within Hueco Mundo can be counted with the fingers on one's hands. The combat capabilities of a Vasto Lorde are above those of the captains of the Gotei 13