I agree with halaros536, you're the only one.
If you look back at some of the other characters, kubo gave us clues of what their abilities would be. Take Shinji as an example, when we first saw him he was upside down, then when he introduced himself he spelt his name backwards and also said that reverse was his specialty. If we look at his release, it matches what was told of him. Also look at Tousen, his releases was translated as cricket, but direct translation was annoying insect or something, so he turned into a fly. Now think Aizen........ Anyone got any clues?
Well, the zanpakuto is after all a manifestation of the shinigami's soul/personality. As for Aizen, pretty sure it has something to do with some kind of liquid or gas, if speaking for his shikai anyway. If I remember correctly, Aizen also tricked everyone into believing that his zanpakuto was water-based and created illusions, so I assume that it is reasonable that it is in fact water-based. The best lies are those that are the closest to the truth after all.
It might just be that he turns transparent if he would have a resurrection and being invulnerable against physical attacks.
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