Board Thread:General Discussion/@comment-4976518-20140808063123/@comment-28044177-20170111184342

ChibiBuu wrote:

Irrelevant, just because he sometimes uses the release command doesn't mean he cannot release his zanpakuto without it. By your logic Ukitake didn't ever reach bankai because he always released his zanpakuto with his summoning chant.

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.

Cocoport wrote: Maybe Aizen never released his bankaï because it's a useless one, unsuitable one or it's overly dangerous for the user.

For example sui-feng Bankai is not suitable for her. And Rukia's is really dangerous because if she make a mistake, she has high chance of dying.

The Soi Fon case was because she didn't have a good relationship with her Zanpakutou. Something that changed after the tiemskip, since she no longer has those major drawbacks. And the Rukia case was because she hadn't mastered her Bankai since she JUST achieved it.