the joke is that Ryusui is so self-centered that he never bothered asking anything about his servant. Gender, birthdate, nationality, full name, etc. are "unknown."

That definitely works a little better, but I like to KNOW, damn it.

I said the same thing about the androgynous Chevalier d'Eon in Fate/Grand Order, back when I played that.

The only exceptions I've ever made are Crona from Soul Eater, and Hansel and Gretel from Black Lagoon, due to the physical and mental traumas involved in all three. Those poor...um, people.