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

- EDITED -

Aaroniero told Rukia that he was the only Gillian who was also a member of the Espada. It basically means that he skipped the Adjucha-level in his evolution, going directly from Gillian to Arrancar, unlike other Arrancars.

He possessed the ability to consume the reiryoku and powers of every Hollow he devoured, making him the only Espada who could continue to evolve infinitely. He could display the appearance, memories and powers of 1 of his devoured "victims" at the time, but when he released his Resurrección, he basically displayed the power of all the 33.650 hollows he had devoured, at once, in 1 huge body.

When he devoured Metastacia's spiritual body after its death, he gained its reiryoku and powers, but he also gained the reiryoku, powers and memories of Kaien Shiba, as they were fused at the time. Since Kaien was a lieutenant, Aaroniero increased his power quite a bit. He also gained access to Kaien's Zanpakutô, and his skills using it, making him a fairly strong opponent in his sealed state.

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Regarding the last question, it's not been stated if Aaroniero was an Espada at the time when Nelliel, Dordoni, Mosqueda and Sanderwicci were a part of the group, but Zommari said that Aaroniero was "the last of the first generation Espada", so it would seem so.