Menos Classifications In Bleach Explained
In the world of "Bleach," Hollows are about as close to enemy canon fodder as our heroes ever face. Numerous and deadly, disposing of Hollows is one of the prime responsibilities of Shinigami (Soul Reapers) throughout Soul Society. Typically, when a human dies in "Bleach," their souls naturally pass on to the spirit world, where they take on a new life in Soul Society. Occasionally, however, these souls do not cross over, and instead they stay in the world of the living and become corrupt. They then turn into monsters that feed on the souls of both the living and the dead unless they are purified by a Shinigami.
Typically, Hollows aren't too much of a problem for Shinigami, but that's just because the grand majority of them never reach the full potential that a Hollow can attain. Assuming a Hollow survives long enough and consumes enough souls to gain more strength, they can become Menos Grande (or just Menos for short). These evolved Hollows are not only more dangerous, but also potentially more intelligent than their brethren. On top of that, there are three distinct classifications of Menos in "Bleach," with each one experiencing an exponential increase in power and ability.
Gillians are the weakest Menos, but they're still dangerous
The most numerous, yet altogether least powerful, type of Menos shown in "Bleach" are Gillians. Depicted as hooded figures wearing spiked masks, Gillians occur when a regular Hollow has combined itself with several others of its kind.
Because it has many minds, and because the minds of regular Hollows aren't particularly sharp to begin with, Gillians are more animalistic than anything else. They live only to consume souls, which they hunt with fervor using their sharp claws and long tongue.
Like all Hollows, they typically only leave their home realm of Hueco Mundo to hunt. If they do so, however, they are liable to be purified by a Shinigami. But not just any Shinigami is capable of the job, and it takes a more proficient Soul Reaper to destroy a Gillian and send its numerous souls back to their proper resting places.
Adjuchas are a more dangerous evolution of Gillians
On rare occasions, one of the many souls which make up a Gillian will gain dominance over the others and begin developing an intellect of sorts. Assuming the individual soul can maintain this foothold for long enough, the Gillian will then evolve into an Adjuchas. These smaller, more uniquely designed Hollows betray their lesser size by being more powerful, often acting as leaders of hordes of Gillians. Due to their greater level of power, only the most proficient Shinigami of the Gotei 13 (or beings with similar levels of power) can go toe to toe with them. However, being an Adjuchas really isn't all it's cracked up to be.
While Adjuchas have the advantage of greater power and keen intellect, they are almost always in danger of reverting to their mindless Gillian forms. If they can't keep up a steady diet of souls, they change back with no hope of becoming an Adjuchas again. On the other hand, if part of them is devoured by another Hollow, then the Adjuchas will remain in their current state, but it also keeps them from ever evolving into the next stage of the Menos life cycle.
Vasto Lordes are about as bad as Hollows can get
Beyond Adjuchas, there is one more type of Menos that strikes fear into the hearts of Soul Society — the Vasto Lorde. These beings are so powerful and so rare that their total population lies somewhere in the single digits. On top of that, it isn't even entirely known how they achieve this form. Some characters, like the Arrancar named Grimmjow Jaegerjaquez, have theorized that it simply takes an Adjuchas consuming a ridiculous amount of souls to become a Vasto Lorde, though this isn't known for certain.
Whatever causes Adjuchas to evolve into Vasto Lordes, they are the last thing in the world you would want to encounter. Even more so than Adjuchas, only the cream of the crop of Shinigami even hope to stand a chance against these Hollow monstrosities. They are so powerful that in Chapter 197 of the original manga, the Shinigami Captain Toshiro estimates that 10 Vasto Lordes (albeit, transformed into Hollow-Shinigami hybrids) would be enough to cause the downfall of Soul Society. Thankfully, that never happens.