Board Thread:General Discussion/@comment-4976518-20140808063123/@comment-11829889-20200705202503

Well, people like Shinji and Hisagi have bankai. They have never used it in the series, but we know for a fact that they have one because Kubo Tite revealed their designs, abilities, their names and even reasons why they went unused in the series. If he can come up with all that for nobodies like those two, then he can easily come up with that for Aizen as well. There's absolutely 0 reason for Aizen to not have bankai.