Hollows Hollows are evil spirits, whom of which live in the Hueco Mundo (Hollow World). However, they can cross over to the Soul Society and human world. A hollow is a plus spirit that has lost their heart, leaving with an empty space to fill. This void is filled by devouring others (living and dead). A hollow becomes what it is from the transformation from a regular human ghost. It turns into a monstrous form, with an obvious hole in its body and wears a skeletal mask. Like the shinigami, the hollows have a multitude of combat skills and abilities. They usually acquire energy to power their abilities by devouring souls, but can also ingest energy from the air when in spiritual realms such as Hueco Mundo. The process of becoming a hollow takes long periods of time but occurs because a Plus spirit is not guided by a Shinigami to the Soul Society. The process however, can be sped up by an attack of another hollow through the use of certain spiritual powers. The majority of ghosts travel to the Soul Society after death, but some stay in the world of the living to fulfill certain goals, such as looking after a loved one, continuing a grudge from beyond the grave, or by protecting a particular location.
Interacting With The Living
Ghosts have limited abilities to interact with the living. They find it hard to cope when their loved ones move on or they are forgotten. They become dangerously obsessed with fulfilling their goals and will even kill anyone who come near a loved one in order to keep them safe. At this point, the ghost warps into a hollow. The masks of a hollow are always white and skull like, but can vary in shape and form depending on the hollow. If the mask is broken, the hollow is able to take on their original form and identity for a period of time. Low level hollows are weaker, smaller and have less powers then higher level hollows.
Menos
When many hollows pile up on top of one another and merge, a Meno is formed. These entities can be enormous and pose a great threat to both the dead and the living. The Soul Society created highly trained strike teams devoted to just handling the Menos. Menos are classified into three categories. Gillian, Adjuchas and Vasto Lorde.
Arrancar
A hollow who has almost completely removed its mask and gained Shinigami powers is called an Arrancar. Originally, only very few hollows were able to actually do this, and their strengths were limited. The process of transforming a hollow into an Arrancar is named Shinigamification. Hollows and Arrancar differ because of the location of their holes, and because of the almost-total disappearance of their masks. The chances of an Arrancar retaining a humanoid form increase respectively to their intelligence levels. If powerful enough, an Arrancar seals its power in the form of a Zanpakuto.
Arrancar who were formerly Menos are referred to as Numeros. Their name includes a double-digit number. They are led by the Espada and are combat specialists. The Espada are Arrancar with particularly destructive powers. They are assigned numbers ranging from one to ten. One being the highest or most powerful and ten being the lowest or least powerful. All other Numeros have numbers based on the order of their birth. An Espada has a tattoo on their body reflecting their number. Espada are the most powerful fighters of the Menos and are much stronger then the average Numero. The Espada consists of nine males and one female. Former Espada who have lost their rank are called Tres Cifras. They are assigned a triple-digit number. However, they are still much stronger then the average Numeros. Exequias are part of the execution division, apparently charged with dealing against intruders/rebels.
Hollows
Ghosts have limited abilities to interact with the living. They find it hard to cope when their loved ones move on or they are forgotten. They become dangerously obsessed with fulfilling their goals and will even kill anyone who come near a loved one in order to keep them safe. At this point, the ghost warps into a hollow. The masks of a hollow are always white and skull like, but can vary in shape and form depending on the hollow. If the mask is broken, the hollow is able to take on their original form and identity for a period of time. Low level hollows are weaker, smaller and have less powers then higher level hollows. 
When many hollows pile up on top of one another and merge, a Meno is formed. These entities can be enormous and pose a great threat to both the dead and the living. The Soul Society created highly trained strike teams devoted to just handling the Menos. Menos are classified into three categories. Gillian, Adjuchas and Vasto Lorde.
A hollow who has almost completely removed its mask and gained Shinigami powers is called an Arrancar. Originally, only very few hollows were able to actually do this, and their strengths were limited. The process of transforming a hollow into an Arrancar is named Shinigamification. Hollows and Arrancar differ because of the location of their holes, and because of the almost-total disappearance of their masks. The chances of an Arrancar retaining a humanoid form increase respectively to their intelligence levels. If powerful enough, an Arrancar seals its power in the form of a Zanpakuto. 
