Board Thread:General Discussion/@comment-4976518-20140808063123/@comment-31121580-20200814095329

Aizen for sure has bankai as the reason he created the hyogoku was to transcendent the limitation of the Shinigami, just how HUmans have physical limitation Shinigami also have a limit so it owuld be stupid for him not to have one.

the only reason he never used it is likely due to restrictions or side effects of using it, like Shinji or Shunsui, if the Bankai removes the effect of Shikai hypnosis than i can understand Aizen never using it. every Bankai used by strong individuals have some type of side effect -> Shunsui cant release it around his friends or else they would also get dragged, Shinji is also the same,  Yamamoto heat is so strong that he could also kill his own team by merely being close to them. past Kenpachi had an AOE the size of a country so his bankai was also restricted from use.