Hollows (info)

Concerning Hollows ( I may have accidentally left out some things. I might be a slightly bit biased towards Hollows)

Hollows are souls that that for some reason couldn't pass on therefore corrupting their souls Hollows aren't actually evil they have an instinctual craving to eat souls to fill up the void inside them although I will point out that a lot of Hollows end up becoming evil due to circumstances the masks that Hollows wear suppress their emotions and a lot of weak Hallows are pretty much just Mindless monsters it is only by devouring Souls that they work their way up the ladder two menos Grande do they regain some semblance of humanity or inhumanity in some cases

The process to of becoming a menos Grande (at least mentioned in bleach that I know of) is that numerous Hollows fused together to become Grande there are three forms of Menos the weakest is Gillian's these are formed by numerous Hollows using together they are gigantic compared to other Hollows they are the most numerous of the menos Grande and generally most look alike it is during this state of Menos that a hollow tries to have a single personality come out on top when it does it begins eating those around it in an attempt to reach its next class of Menos which is the adjucha they are smaller and far fewer but far smarter and stronger than the gillians to the point where they're usually command gillians into battle and generally take the shapes of animals and finally we have the most powerful type of the Menos the vasto Lordes they're roughly the same size as humans generally and very few in number most can't even hope to fight against them.

A possibility thing than anything else for gillians as they are made up of multiple Souls a male Hollow before becoming a Gillian can become female afterwards due to a single personality coming on top the reverse is also true they're also is another thing that you should understand is theoretically speaking anyone who has been eaten by Hollow can come back as a Menos Grande due to what's mentioned above though there are some circumstances involved that would either allow or not allow this to occur as long as the memories of said person are intact or the soul somehow managed not to be completely devoured