Board Thread:General Discussion/@comment-4976518-20140808063123/@comment-11829889-20170321173204

Khaotic Twist wrote:

Difference is that we KNOW Ukitake has a Bankai. Since it was stated that achieving Bankai is a requirement for becoming a Captain and it was stated that no Captain in the history of SS has never achieved Bankai with the exception of Zaraki(who eventually achieved it anyways). Aizen faked his powers while in the Gotei, so him actually having a Bankai is unknown. Him being able to release his Shikai without a chant would greatly indicate that he does have a Bankai. But unfortunately we've never seen him do it, so we're back to square one.

Aizen wanted Hogyoku to surpass limits of a shinigami, therefore implying he has mastered every way of shinigami martial arts, including zanjutsu, therefore that is invalid.