Visuals are cool and unique! Music is solid!
I did encounter a bug where the screen went completely white except for textboxes, making the game unplayable. I think it had something to do with minimizing/maximizing/unfocusing the game window at the wrong time.
I don't play many rhythm games, so my eye/ear may be off, but I feel like the visual indicator for pressing a key to the beat doesn't work well for me (at least without much practice). Unless I'm mistaken, the "notes" approach the center of the bar at a fairly constant speed, but then they suddenly slow down before hitting the beat dead center. The notes also go behind the center bar instead of overlaying it, so the visual cue is less intuitive than something like "this circle perfectly overlays this other circle" or like in Undertale where you're supposed to press the key when a line is centered between two other lines. Once I relied more on audio I was able to get through the tutorial.
Not sure if there's a way to save, but I definitely should have checked, because replaying the whole thing from the start after suddenly losing the second battle was disappointing.
Overall, I'd push through my struggle with the battle gameplay for the art, music, story, and overworld gameplay. I like how the story is mysterious. I enjoy the character voices; they remind me of the Mario & Luigi RPG games (though I haven't actually played those).