I like the idea. I'm not a big turn based combat fan since it's often "tap A until you win except for some bosses then proceed to run in the grass to grind again". But I do like Undertale with the bullet hell twist and Mario&Luigi with the 'active' combat system where you have to press buttons to a timing to maximise the damage and dodge attacks. I would totally play a RPG where you's have to hit keys on time like this one, I think there's a great potential!
Now I think Dogtopius already said pretty much everything about the balance, the lack of tutorial, etc, so I'll just add two things:
- it's really hard to get locked in with the beat because the division is not regular at all. I'm talking about both songs, the base theme and the attack theme. I think it should be simpler, more straight forward, like a good old 4/4. I like the music, it would fit a Final Fantasy battle, but not a rhythm game.
- it's lacking some more visual indication of the beat. Anything pulsating, flashing, glowing, to show where's the beat, and help getting locked in with it.
Anyway, really liked the idea, I would totally play a game like this!