User blog comment:Soulreaper1234/Urahara says Fusion Aizen says Subdue/@comment-1853786-20100514145044

"During Urahara's time in the Research Institute, an answer was sought on how to strengthen an individual's soul, the answer being for a Shinigami to gain Hollow powers through Hollowfication. This led to the development of the Hōgyoku, though once he had created it, Urahara immediately placed a seal upon it when he understood how dangerous it was." but why was it dangerous? So far it has done what? make Arrancars and transform Aizen though those events were dangerous that is only because it got stolen. So why place a seal on it

So yeah my money is on fusion and that the Hogyoku is gonna take control of Aizen and it probably won't be able to access his Shinigami powers.