Hmm...I don't know how to put it. There's something about Mizu that's very serious, and that's why I feel she does well with really elegant musumeyaku like Tonami. Ume-chan is more the cute/spunky type. (Obviously both Tonami and Ume-chan are very talented, just in different ways).

That being said, I'd certainly be open to the idea of Mizu/Ume-chan in an alternate universe. If anything, it would have been interesting to see how that would have made Ume-chan grow as a performer.