In article  Drew Ward <we436@freenet.victoria.bc.ca> writes:

Ranma didn't know what to do, so he just copied what he saw from his mother 
and sister (of course, Nodoka did it purposefully while Ranko is just 
uninhibited) and what felt good at the time.

He was ashamed because of the stigma commonly attached to masturbating and the 
fact that he had done it as a girl.  Ranko had done the same thing in her 
cursed form, but it neither had a place in the story nor is she ashamed of it.

Ya know, what are the chances of something like that actually happening?
Mother-daughter quality-time masturbation?

Nodoka did it to have the twins be comfortable with the idea of both sex and 
their bodies, though it took more with Ranko than Ranma.  Nodoka and Genma 
made love in front of their kids, as was written in the fanfic.

Ranko is extremely uninhibited and forward, and hopefully this will come out 
in later episodes.

JK