[Discussion] I've been thinking of something

[Lord Tywin]

I remember Aizen saying that a battle between shinigami is a battle of reiatsu. And this was how he overcame Sui Feng's bankai. Now do you think is it possible for a shinigami with greater reiatsu than Aizen to overcome his shikai or bankai?

 

[Tantalus Thief]

When Aizen puts you under KS you don't realize it so unless the rieatsu overpowers his rieastu before the hypnosis is casted. I think Ichigo and the guards are the only Shinigami with enough power.

 

[Mahesvara]

Yamamoto couldn't do it and so far no one has been shown to be able to break it. Honestly, I think only transcendent beings, like Aizen himself, can break it. Which includes Dangai Ichigo and current Juha, but we haven't seen him use it on people that are on that level so I can't say for sure.