Board Thread:General Discussion/@comment-4976518-20140808063123/@comment-6019258-20140811034040

Complete hypnosis is his bankai. The running water type (that creates illusions and tricks enemies into attacking each other) that Isane mentioned when she and Unohana first discovered his secret was his shikai. It just so happens that the shikai has to be be observed for the bankai to have any effect. He did say to them he was going to show them the true form of his zanpakuto, and I always thought when somebody talked about the "true form of their zanpakuto they were talking about its bankai state...ie "complete hypnosis". I'm not trying to be an ass like I'm certain this is the case, but it's a theory I've had for a while.  I don't even think Kubo thought about this, but I wouldn't be surprised, if pressed, something like this would be his explanation.