Whoa! O.O I just thought of something that would be hilarious for Fai to call Kuro:
"Mrs. Flowright"
O.O... Don't ask me what made me think of this... Sadly, I can't think of a way that would work in Japanese, since they use -san for Mr-, Miss-, Ms-, and Mrs-... However, there is always "anata"! (Normally means "you", but women often call their husbands "anata") Which would be a cute thing for Fai to call Kuro!