I've been reading this thread and its gotten me thinking.  (My RL friends look
scared when I say that for some reason.)  If your idea has been done before,
look at how it's been done, and do it differently.  Take splitting Ranma's for
instance, I can think of two new ways to do that story:

1.  Ranma is split into boy and girl halves.  Both of them seem strangely
weakened.  Cologne announces that the life force of one person isn't enough to
keep two bodies alive.  Either the two Ranma reunite, or both of them will
die.

2.  Ranma finds a magic mirror/pool/reflective surface that can cure him by
captureing unwanted parts, but the magic of Jusenkyo causes something strange
to happen, it causes the captured reflection to have a magically created body.
Shortly after Ranma leaves, Ranma's girl half steps out of the mirror.  As a
reflection of Ranma, she has the same feelings towards herself that Ranma did.
As a result, she hates herself and wants to die.  But she cannot die unless
Ranma himself does, so she systematicly tries to destroy everything Ranma
cares about, to induce Ranma's sucide.

Two Ranma splits that are, as far as I know, totally original.

SlayerNext@AwOL.com
"Koala!"