Super fun little game, I really enjoying the mixture of the fights with the rythmn game.
I would say that the display of the keys could use some work, sometimes the keys on the right would clip behind the "hp bar" making it harder to see, and also if I was paying attention to the one on the right I could barely see the ones coming from the left in time because they are just white and away from each other.
Aside from that maybe adding a sound when you successfully hit the key would help with player feedback.
Anyways, really nice job :)