Board Thread:General Discussion/@comment-4906037-20140311111448/@comment-5780397-20150920174758

Mimihagi stopped Ukitake's illness from killing him, although it did not heal him. Though I doubt we'll ever get to see his Bankai (like Aizen's, sigh), I don't know the details, but I think it is something that allows him to attack and defend at the same time: I imagine something like a stationary barrier with the ability to deflect energy attacks, like his Shikai, while he is able to attack from behind his shield with omnidirectional beams. However, Bankai are always much more original than what I can think of, so it is unlikely this will be the case.