This question is something to speculate about.
There is another thing which bothers me, which might be not very easy to answer.
By the way, has someone noticed this before?
Rika always says "Mi-", Hanyu always says "Au", which makes "Meow" together. So I think it's a game between both of them. Everytime Rika says "Mi-" to someone, Hanyu adds "-Au" (which of course can't be heard by most people until Matsuribayashi).
Maybe this has been known before, but I never read it anywhere so far.