Sailor Galaxia and Princess Kakyuu, after she is back to normal. I think Galaxia's true personality is stoic and introvert but dominant. It would create an interesting dynamic with calm benevolence of Kakyuu. Plus Galaxia's guilt. Bonus for making Kakyuu's trio of guardians absolutely lose it when they find out.
“You are a firm believer of not letting a little thing like the creators saying two characters are related to get in the way of seeing the chemistry, after all if it worked for “Amara & Michelle” why not them?”