I guess no gender differentiation. And Emperor sounds badass. Empress kinda sounds like she needs a man.
Its the proper title for a ruler. In England Queen Elizabeth was a Queen but her wife Philip was entitled as Prince Philipi and not a King and the next line for the throne is Prince Charles when he became a King he will be called a King but her wife Camilla will only entitled as Queen consort. The title of Queen/ King / Emperor are titles for the ruler while the title of Queen consort, Prince consort are titled for the wife or spouse of the ruler.
Since the MC of this story was a ruler her proper title should be Emperor since she was a ruler. The title of the empress is only used for the wife of the emperor or a wife of a ruler. That's why in some stories The emperor always have an empress consort and queen consort or they even had mistresses known as concubines. Well in other stories they prefered to use the title Empress.
Giving more info~
Furthermore, in history there's a tendency to always make the ruler masculine, even if they are a woman. There's a speech made by Queen Victoria in which she referred herself as a man or as a King, I'm not sure now. Women in power were either mascunilised or destroyed because society couldn't believe or think that women could wield power because they were women.
The "emperor sounds badass while empress sounds like she needs a man" comment is fruit of this tendency to man= powerful woman=needs man. It's just a result of years and centuries of patriarchy, specially in power.
So, if the story was a real one, the reason why she's an emperor is because society didn't think a woman should be the ruler, but if that woman was not an empress but an emperor... They could accept it.
Oh I see, so empress is only used for the wife or spouse(?) and emperor is like the more formal and must be used term for the ruler?
Lol now that U said it like that... kinda makes sense ╮(￣▽￣)╭
Why is it named emperor not empress?