Board Thread:General Discussion/@comment-6057702-20130802173149/@comment-11051098-20130802210716

Aaroniero told RUkia he was "the only Gillian who was also a member of the Espada". I understood that he was still a Gillian.

He said that he gained Metastacia's ability of consuming the powers of every Hollow he devoured. I think that's why he was an Espada while still being a Gillian. He probably found a way to gain a human form and size, maybe due to Metastacia's powers, and managed to maintain all the power he had, and continued to devour, into a human size body, which could have made him strong enough to become an Espada.