It's an extremely old fic, that was never really completed, but took on a very interesting plot principle: Ranma falls into the spring of drowned LITTLE girl. As in, five years old little girl.
http://jusenkyo.wikia.com/wiki/No_Fair
Here's a link to the most complete copy of it.
I read through it all, and while it had an interesting premise, does anyone feel like it may be a little extreme? Kasumi is completely determined to see Ranma end up as nothing more than a little girl, and based on his situation, Ranma dislikes it but doesn't seem to want to tell her no.
What do you think?