Simoun is an anime set in an alternative world in which ever infant is born into a female body. Males still exist, but how they come about differs from country to country. In the nation of the main characters, children go to a spring when they are 17 (though some may postpone under special circumstances) and declare a gender. I they are undecided the keeper of the spring chooses for them. Gender balance is maintained.
In the first or second episode, a character accompanies a friend to the spring. The friend is undecided on the way to the spring. She is still so as she moves through the waters, prompting the keeper to choose. She leaves the spring a man. When the character calls her friend by her new male name (basically, just add an F because all male names end with an F), the friend breaks down into full-bodied sobs.
Here are the interesting points—
(1) While the friend was contemplating her choice on the train to the spring, she noted that being female would be nice because that is familiar, but that male would be nice since she’d have so many more opportunities. At first this irritated me. After all, you’d think that in this sort of world the genders would be more equal power-wise.
Then, as I watched others in the show consider the choice, I realized—a lot of the girls need an incentive to become male. That might be romance (seriously, show?) or job opportunities. Being female is comfortable, familiar. They’d not change into someone else.
(2) In several scenes, characters note that they are neither male nor female. Their bodies are female, but they are not set into any gender with all its rules and roles. Romance between the girls can happen, but there is the expectation that one will become a male eventually. Or that the romance isn’t serious because they are just children. (Even so, when one character loses her girlfriend (very first ep) her grief is treated seriously, though not all understand it).
In this show, gender is not biological. It is not set by the body.
(3) This is even more evident with one of the mechanics. The mechanic has long hair and prominent breasts, but when called by name, the name ends with an F. She is a male. The transition from the girl body to a boy one is not instant. This character has been male for over two years, but still appears female to a viewer. The transition takes time. The body is not instantly stronger or more masculine. Even the voice takes time to deepen. Those who appear the most male are inevitably old and/or are fathers.
(4) And, yet, the characters know. The friend, upon leaving the spring, knew she had become male. The change is first intangible, but certain. The knowing comes first. The body shifts to adapt after.
So, Simoun has created a society in which gender is something you just know as well as a constructed place within the culture. I think this is true for our world as well, but they’ve made it more evident by separating out the body and appearance.
(5) Anyway, I am writing all of this from a cis perspective. Plus, I’ve only reached up through the diplomatic mission episode. I’d really like to see a trans take on the series.