idk what the original text says but this is set in the human world (they're not as free with their identities as the demon world) and everyone has only just met Opera so maybe they don't know yet.
Third person pronouns aren't used as often, and are gendered less often.
That's why Iruma could not know, conceivably.
Here he isn't confused, because they need to go to the doctor's and other annoying bs.
It's people not as close that don't know.
They use a basic, neutral first person pronoun. Many of all genders use it.
Makes things hard for translators, and changes a lot of how different stories flow.
In Japan, saying "I" is more likely to tell someone about your gender than someone indicating you. More likely to use their name or title, and then "this/that person" is pretty common.
One's own speech patterns will have more gendering than how anyone else refers to you.
First-person pronouns are a wild spectrum of signalling various things. 52 of them.
There is so much that is absolutely untranslatable. "Kakkoii onnanoko to 12 cm no yakusoku" or something like that has a girl who not only dresses like a guy, but uses a traditionally-masculine pronoun, and very traditionally-masculine speech patterns.
It's the trendy straightgay thing, except the guy is masculine, too, so they appear gay to those who don't know them.
But she's not doing anything to say she is a man. It's just... made very easy to infer. That just doesn't translate. The whole dynamic changes, because Indo-European languages don't work like that.
Other languages I know are pretty heavily gendered, so that's moot. Chinese wasn't very gendered, iirc, but it was too hard.
