This just isn't confused enough, and you're not using enough series. ;)

You need to muddy the waters a bit, something like this:

Rei and her grandfather have an old well out back, into which
Ranma unceremoniously falls.  Climbing out, she finds herself
in some medieval-looking land.  A rotund, middle-aged waitress,
astonished, identifies Ranma as the reincarnation of her long-dead
younger sister, a sorceress.  Nailed to a nearby bodhi-tree is
a half-demon, half-golem, half-monster smartass who thinks
_everything_'s a secret, and who follows Ranma back through the
well into real life.

Also, Usagi needs a cute blob mascot named "PQ" and a suit of
mobile power armor, or maybe a small tank, but with a cute
name.