This is a fantastic idea. I got hooked into the game very fast LOL I think there's so many directions you could go with this. I think the best is that the systems and mechanics are in place, and they flow so well, I really enjoyed the transition between the two characters. Good music and SFX, and adorable art.
The game would really benefit from a tutorial level, and the adventure mode character could have a bigger role in the game overall (for instance, giving health to the fighter one). Great play at the theme!