Board Thread:General Discussion/@comment-4976518-20140808063123/@comment-27917224-20160305012916

Aizen does have a bankai. It was actually one of the first we ever heard of and it was described in detail.

It is/was the flowing water he showed the other captains. While it's been a long time, I'm sure plenty will remember that the flowing water ceremony was the trigger for his absolute hypnosis power.

The effect of his bankai is that those effected by it are affected for the rest of their lives and that he has full control over all of their senses.

He would then use his shikai to control the illusions.

This is also why during the battle in Karakura town when Aizen swapped himself out for Hinamori and the captains started going after her, ichigo shouted "what the hell are you guys doing?" He was totally unaffected by the illusion because Aizen had never used his bankai on ichigo.

The only reason a lot of people don't realize what his bankai was, is because there was no scene of him saying it and odds are that he didn't. The only reason the characters say 'Bankai' is for dramatic effect, they don't actually have to say anything.