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
Based on the artist's most commonly drawn characters from the series, I suspect this might be an aged up interpretation of one of the builders. Though, I cannot tell if this is the male or female one.
Edit: Found out through some of the artist's other work that this is meant to be an older version of the male builder!