(I definitely didn't get this idea from a fanfic. Also, this is wlw. it'll become obvious why in the description)
In a world run by kings and queens being the heir to the throne is an important job. Character A knows this. she is the heir to a small outdated kingdom. Her parents are old fashion and plan on her future husband being the one in charge. That's why when she turned 18 they looked for a suitable suitor. She hasn't had much luck until they found Character B. Character B is apart of the royal family for a much larger and less traditional kingdom. They are far behind when it comes to who is in line for the throne since they have so many siblings. Most of the interactions between the rulers of the two kingdoms about their arrangement were via mail. This is a bit of a problem when you take the fact that character B's kingdom mainly formally speaks and writes in their own language that Character A's parents are very rusty in. That's why when character B showed up at Character A's castle they were a bit shocked and confused to find a princess instead of a prince.
I can be either character. I have an idea for character A but I'm also fine with being Character B
Warnings
-Possible chance for abuse(especially if i play character A)
-misogyny and homophobia
-I think that should be it