Major spoilers! Try and beat Rose and Camellia at the hardest difficulty first, as the easter egg awarded at the end is worth all the effort. Plus it's no fun watching when you can play the game yourself.
I'm beginning to think that each opponent has an "outer target circle" for normal hits and an "inner target circle" for critical hits. Unfortunately, I can't seem to figure them out, and I can barely hit the second opponent at all.