Honestly, while Yuri went way too far with what she did, Kai himself is also to blame. I don't know how old he is anymore (or Yuri for that matter), but that honestly doesn't matter, especially to Yuri. Because she sees him as the King of their country, and a King has to produce heirs. They're old enough to start working on that, at least. Kai is being stupid.
I don't think that romance/harem is off the table or anything, but it's clearly going to be a while before we have that sort of development. Which is dumb.