The Double Standard of Unsettling Gender-Reveal
We all know the double standard of the trope: When a character who we assumed to be a man turns out to be a woman it's played for Fanservice and it's supposed to be hot. When a character who we assumed to be a woman turns out to be a man it's played for squick. Why? To answer the question this troper would like to use the two most well known examples: Samus and Bridget.
In Metroid, Samus wears a non-gendered outfit that fully covers her. There's nothing indicating the gender. Now, since this was The '80s and there weren't many Action Girls everyone asumed that it was another space hero without considering that maybe she was a girl. Plus, most of the times to indicate a character under an armour is a woman they tend to give her a Form-Fitting Wardrobe that, even if it doesn't make sense, tends to show Hartman Hips and Most Common Superpower. Think of Natasha Irons as Steel. Plus, since it was a bloody 80s videogame there wasn't much room for dialogue or voice acting, or anything that would indicate a personality, so it wasn't farfetched to assume it was just another stoic Bobba Fett-esque clone. The combination of these factors it a surprise when it turned out to be a woman, since the gamers of then weren't familiar with badass action girls.
On the other hand, Bridget in Guilty Gear dresses in a feminine nun habit and has a stereotypically female attitude. Since transvestite/gender-nonconforming representation is sadly scarce, it doesn't cross a gamer's mind either that she might be a Wholesome Crossdresser. And, since Creepy Crossdresser is a thing, more close-minded people were uncomfortable with the reveal. Plus, there's the fact that while Samus is widely presumed to be cisgender, Bridget is canonically a trans woman.
In both cases the reveal serves as a Fair for Its Day subversion, but the key in that the first one isn't as unsettling as the other is the presence of stereotypically gendered characteristics in Bridget and the lack of these for Samus, combined with some hints of transphobia. If Samus had been a broadshouldered deepchested stronglimbed frankeyed redhaired freelyfreckled shaggybearded widemouthed largenosed longheaded deepvoiced barekneed brawnyhanded hairylegged ruddyfaced sinewyarmed heroine there would have probably been a similar reaction to the reveal that she's a woman. It all boils down to traits we assume only belong to a gender used in the other.
