On Tue, 24 Feb 1998, Scott Schimmel wrote:

	Actually, there's a small problem with that... he didn't wish
for Belldandy as a fiancee, just to have a fiancee who was that
understanding.
	When Keiichi made the wish, Bell twisted it a little, due to
their past history, but there's no reason she should do the same for
Ranma... right?

That was anime-only, as far as I know.  I don't think they have a past
history in the manga.