Stray characters not in the origional cast are subject to the same
complaints; the character is really the author.  I don't totally subscribe

Hmmm... Does that mean that Miyabi is me at ... toddler age? Wow...
Cool, I always wantd to be Ranma and Akane's kid! Hmm... maybe I'll have
Miyabi go marry Ryouga or something just to make my dreams come true,
and write an even hotter and steamier lemon scene between the 3 year old
and Ryouga-kamisama!!

I doubt that even you would have had any use for Ryouga at Miyabi's age.  
Except of course as a pet piggie to cuddle (as seen in your fic :)

Awww... but doesn't the author's alter ego HAVE to have sex with all the
characters they like?

Kun-chan...