I thiiink this is meant to evoke Ranma 1/2? Become a girl with cold water, become a guy with hot water, as represented by the eyelashes and chest disappearing? Not sure how to go about applying the relevant tags to such a case though, if others agree (such as, do we add genderswap (ftm)?)

Edit: commented that, edited it for context, and in doing so kind of answered my own question haha; think it would make sense to add such tags even if the implication is that her default state is male here