Really nice mechanic! I will say theme wise and mechanically it mainly feels like I'm just parrying with a different look, but that's okay.
The difficulty spike at the end felt great, I died and immediately wanted to try again which is awesome. I'd suggest setting the respawn point back to the start of the game, adds more weight to the boss fight and incentivises players to improve in the rest of the level. Something to consider.
But yeah, boss fight super fun, if a little easy to cheese one you figure out you can just stand in a safe position and time your left clicks.
A little more polish on the audio and animations would be lovely, but in 48 hours this is a real impressive. Great work!