Hollows

Souls who have died with powerful emotions such as regret or sadness and have not released it in dying turn into monsters called Hollows. Hollows eat other souls to survive. They can be purified by Zanpakuto.

Menos
Hollows that have eaten 100 souls turn into Menos. They gain the ability to fire Ceros and extra power. There are three classes of Menos:


 * Gillians - The first and weakest class. They are pretty much living black skyscrapers. Eventually, if the conscience of one of the eaten hollows overtakes the other consciences, the Gillian will keep evolving by eating other Menos.


 * Adjuchas - The second class. These guys are plagued by the fear of regression, which means if they stop eating they will regress back to a Gillian, never to regain conscience again.


 * Vasto Lorde - The most powerful class. Their power rivals that of a captain's.
 * Transcendentes - A seperat Transcendant class that appeared because of mutatuions in teh atmosphere of Hueco Mundo.

Arrancar

 * If a Meno's mask gets ripped off, they will transform into sentient beings known as Arrancars. These Hollows gain Zanpakuto can use Shinigami-type powers.