Quick, how do you get out of a beating/flogging/magic bombing? Be creative.
I tell her to stop and that this is okay. Japan has an ancient tradition of mixed nudity and it's only recently that this has become unusual due to the imposition of western standards. As good Japanese people we should embrace our heritage and accept that this sort of thing is fine.
Being the cool guy that I am, I wouldn't be part of a shit show like the one you are describing.
Scream as if she's the one walking in on me then punch her and tell her to check her anime heroine privilege.
If she touches me I'll sue her for harassment and file a restraining order.