The thing that makes the relationship between Mika and Miria less squicky to me is that, while Mika plays up the whole "sexy gal", woman-of-the-world, playgirl image – on stage and off – she is in fact quite innocent. (This is mostly played in the game commus and the comics in how much she'll kind of self-destruct in romantic situations, and how Rika thinks she has all kinds of experience that she just doesn't.)
