Board Thread:General Discussion/@comment-28096256-20160413001736/@comment-27392440-20160416204323

I hope you don't mind if I post my own theory on this as I've given this some thought too (though I admit this is just speculation on my part and might be overthought a bit).

There are 2 key things I think are required to reach vasto lorde status besides a base power level: being able to enter your inner world and perhaps a special "diet".

Entering your inner world would probably be crucial so you can "digest"/kill the hollow souls you've eaten so you can make it your own power rather than merely being the power of a mass of hollows that are trying to drag you back into the collective conciousness of a gillian (which would explain a vasto lorde shrinking as them becoming their own being rather than a huge composite of many).

The idea of a special diet affecting their growth came when I wondered if anything special would happen if rather than eating other adjuchas they ate pwerful shinigami or even a vasto lorde somehow. Going after especially hard to get souls would not only give an evolutionary push but would also nourish them in a unique way from other hollows and would likely push them to the next stage.

There may even be alternate methods to feeding on others as Hallibel and her fraccion (in the anime backstory of her time as a hollow) tried to never kill their enemies if I'm not mistaken, yet none of her fraccion regressed to gillians or looked like parts were eaten to stop growth. Starrk/Lilinette may even be an example of growing by learning to communicate and bonding with your inner hollow, much like shinigami and zanpakuto do.

I have a much less clearly defined idea for segunda etapa but Ulquiorra may have hinted at it when he said he'd show Ichigo "true despair"... I think he meant his own. Seeing as hollows are born out of pain and emptiness, it's possible that to reach segunda etapa you have to embrace the hole/aspect of death/pain that made you a hollow in the first place (and maybe train too), which may risk soul sacrifice and would definitely inflict soul breaking agony on yourself (even Ulquiorra looked far more sorrowful after after using segunda etapa), which is something that most arrancar were likely not willing to risk making Ulquiorra seemingly its soul user.