I have seen two fics adressing the question on why Kasumi is almost
always calm.  Heres part of the spin on this fic It is her mothers spirit,
in a way.  A tradtion of her mothers family is passing of the spirit.  It
imbues the chosen, Daughter-Heir with a small part of the abilities of all
her predecesors.  now heres where the twist comes in.  Kasumi falls deathly
ill, and is forced to pass on the spirit to some one else.  Unfortunalely
the only person home is Ranma.  When the time comes.  Soun is under
sedation, as is Akane.  Nabiki is locked in her room, and Genma just won't
work.  The way the spirit works is while it is bonded for the most part it
can detach for short periods.  This is how Kasumi always has good advise.
The spirit speaks to her, and she passes on the wisdom.  Now Ranma has a
major problem being the first male to have the duty.  Well male half the
time.  The spirit while mostly good has a problem with boy Ranma.  After A
few days Kasumi Starts Recovering, but There's a complication.  The spirit
can't be given back.  Ranma is subtly influenced over time, and becomes
increasingly different, while still wanting to be male small changes are
taking place. He's calmer, more patient, and is more willing to show his
feelings, problem is Kasumi is haveing problems dealing with her emotions
with out the help of the spirit. Ranm,a unfortunately has a small problem he
can't give very good advise it just isn't him.  How are they going to deal
with Ranma as he changes, and Kasumi.  Over Time Ranma becomes More well
balanced, but has some major changes in his thinking.  When he see's a child
being hit or abused he steps in with out thinking.  Kasumi starts haveing
temper problems, and MAJOR mood swings.  Ranma becomeing more pprotective,
while Kasumi Hovers one edge.  Finally he starts listening to the advice
from the spirit more closely, and trying to help Akne's eldest sister.  This
of course sets Akane off because she has no idea what is going on.  You
could take the story almost anywhere, but I was thinking of a Ranma Kasumi
match-up.  With a few intresting changes.  While Kasumi and Ranma would have
kids Ranma would be a surrogate mother for Kasumi because he can handle pain
better, but also because of Kasumi's unbalanced emotions.  I was thinking
that the only times when Kasumi is really stable are when Ranma is near by.  

It would make thing intresting.