Final Ultima

I still say that Aizen is the villain, he wants to become God and he alone wants to stand in heaven. We even see in the flashbacks how Aizen was scheming from the start. Dude's dialouge always involves only him retaining valid information (like his discussion concerning the Royal Kings) and when he noticed something about Urahara we see the suspicious look in his eye's and not too mention the thing about Gin (Obvious recrutiment). Heck he was even hiding listening in on people's conversations.
Aizen set this up all himself fella's I highly doubt there is anyone else pulling the strings in my opinion.

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Hiro Nakamura

Gin i tell ya, its Gin.....

he seemed to be truely evil at a young age.... Aizen aint got shit on that silver haired, smiling, sword extending (and who knows what else extending) badass mofo

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Final Ultima

Yeah, Gin is just a beast!

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writi

Sorry but i just cant believe that Urahara could become a villian, mainly because he's one of my favourite characters.
IMO either two things are gonna happen:

1. Aizen is the ultimate villian in Bleach and the series will end with his defeat (unlikely)
2.A new villian who is much more powerfull than all the previous main villians, just like all the other shonen animes out there and the series will continue way after the Aizen saga is finished. (extremely likely)