This is an idea for a story taking place after the end of the Ranma Manga. Its not too hard to notice that part way into the stories Dr. Tofu's never really involved at all any more. What if the reason he left is because he fell in love with a woman not involved in the Ranma stories?
The story starts with Kasumi and Nabiki on a shopping trip for things Kasumi couldn't normally find in the local shopping district. Getting additional things for the house etc. And on this trip Kasumi finds out about Ono Tofu's new life and wife. Needless to say she could have taken just about anything better.
Ono no longer acts silly around her and she realizes she doesn't even know the man that apparently everyone else in Nerima got to know. To top it all off he has kids on the way. And insult to injury he invites her to be their God Mother.
There are allot of ways this could be played. But I'm open to suggestions. And should Kasumi's personality or behavior change in reaction to this? Would she go into a rebound situation? How would the rest of the family take the news?