There are many universes, and many possibilities. In one, Kasumi turns into a cat, and marries an english teacher. In another, Kasumi goes to Jusenkyo with Genma, gets cursed to become a boy, and becomes engaged to Ranma, while Ranma stays home with the Tendo's. What if those two Kasumi's switched places?
Frost is looking for a way to get rid of Kasumi so she can have Shampoo to herself. She's going to send the Kasumi of her (A Scary Thought) world to another dimension. In this case that of A Different Viewpoint. Unfortunately things go a little wrong, and ADV's Kasumi comes through to the AST world at the same time. Also Frost gets stuck in limbo...