Just a friendly bit of advice: Don't speak authoritatively on historical matters you lack the intellectual courage to actually learn about.
Trans people are not some modern invention or whatever transphobic garbage you're suggesting here. Hiro's story seems to take place in pre-nazi Germany, which was in fact at the cutting edge of sexual research and queer rights advocacy from foundations such as the Institut für Sexualwissenschaft in Berlin (the very institute whose books were the first the Nazis gathered for book burnings, fyi)
Hiro's identity isn't forced, it fits well with the story's period AND he is precious and I would kill anyone who would try to harm him.