Board Thread:General Discussion/@comment-6057702-20130802173149/@comment-14757951-20130912104931

Sternritter M wrote: I dunno about the manga, but in the anime, 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, and that this power made him the only Espada who could continue to evolve infinitely. He probably found a way to gain a human form and size due to Metastacia's or Kaien's powers, suppressing all the power he had into a human sized body, and that's probably how he became strong enough to become an Espada despite being a Gillian.

I think he also said that the form he gained upon releasing his Resurrectión, was a result of the 33.650 Hollows he had devoured. Sort of an army of 33.650 Hollows in 1 huge body.

Nope. The ability to gain the Reiryoku/Reiatsu and abilities of any and all Hollows that Aaroniero eats (and his infinite evolution) is all his own ability that he's always had. Metastascia could destroy Zanpakuto's one a night and fuse with another spiritual being (like a Shinigami). Aaroniero ate Metastacia, who was still fused with Kaien (although it's unknown if this happened before or after Aaroniero became an Arrancar/Espada) and thus he gained both Metastascia's abilities (mentioned above) and Kaien's (Shikai, Shunpo, Kido, everything).