Well, for the mimic fight, I'm using Circle, Mikuru and the robot because that's what you're forced to do. As a general rule, I've been using Circe, Mikuru, and Kiki. I use Kiki to buff everyone and I try to use Mikuru and Circe to do damage. The problem is that it feels like everyone does so little damage unless the enemies are debuffed and you target their weakpoints. I finally managed to get mikuru an ability to lower fortitude so maybe that will make life easier. Not to mention the turns when you don't have enough rage/focus/whatever to perform actions