Hueco Mundo was once a wasteland, a rolling desert that seemed to never end. no sunlight, no warmth, just a desolate depressing wasteland. But over the last thousand years things have been changing.
A group of hollows, both vasto lords and arrancar, took it upon themselves to change things. no Hollow knows why, but they have built a grand city, with several districts, that is spreading through Hueco Mundo. It's current size is greater than any other city in exsistence, but ti still covers only a fraction of the wasteland.
Many hollows have gathered there, under their leader's rule, and such closeness have caused an increase in normal hollow evolution, because food is readily avaliable. Any gillians that are found are removed, and taken somewhere, grouped together and forced to feed on each other, they evolve quickly, and become adjuchas.
This rapid increase in high level hollows has apparently been noticed by soul society, but they have no idea what is happening in hueco mundo.
