When the suit, which is tight enough as it is, suddenly has a person in it who >has twice the mass of the usual occupant, something will give.

Twice? Maybe an extra 20 to 50% but twice? The only two sex-changing characters in Ranma were Ranma and Herb. In neither case was it shown that they lost half their mass when they turned female. Also, there are plenty of pictures of Ranma-kun and Ranma-chan posing together, you can tell that Ranma-chan is definitely more than half the size of Ranma-kun. About three-quarters actually.

BTW, I think it might be prudent if Mackie and Linna's hardsuits were modified to reconfigure themselves if the wearer got wet. Like expanding a little?

Finally, I must say that the first three paragraphs of this chapter very poetic. Not bad.

P.S. I just noticed something:

    He stared, wide-eyed, at what...was...the door. 

Grammatical error, change the "was" to "had been"