Really fun! Enjoyed it a lot, played through it three times. I think this is a great start to a fun minigame or could be the beginning of a great rythm game. I would be compelled to see where you can take this with a second song and some more creative ideas.
I think some silly sfx, particles, tricks and showy flashes and overall "juice" might make it a more interesting scene. For example, when you lose HP, take the chunk you lose off and make it fall off screen instead of just draining the bar. You could add sound effects to getting hit, or charging. Make you or the opponent flash and emit particles and in general give more feedback to the player for hits/blocks/charging will go a long way.
But all together, a very tight, well made, fun jam game. Good job!