So Aizen is the only TB in BV (exept Ichigo's family)..right...?A Shinigami didn't defeat Aizen Ichigo did a fellow transcendent being...duh, Urahara's Kido had no effect on Aizen when he had Transcended it was only after Ichigo pushed Aizen so much that the Hogyoku rejected him did Urahara's Kido take effect.
The moment the Hogyoku rejected Aizen he stopped being a transcendent being that's why Urahara's kido finally started to work...you should know this if you read Bleach
These 4 pages explain this...
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The moment the Hogyoku rejected Aizen he became a normal Shinigami again hence the reason why he started to lose his hollow appearance.
I thought that Isshin can use FGT just like Icigo ....