Fun little game! Looks and plays nice, though a little on the easy side.
Interesting gimmick with the hex blade (I haven't seen it before), but not very fun nor implemented well. This is a hack and slash game where the central mechanic is to punish you for hacking and slashing... huh? That's not fun. On top of that, the vulnerability window of most bosses (with the slight exception of the centipede) is so short you're in no danger of draining your curse bar even if you attack nonstop. So what's the point? You've taken very standard boss patterns with alternating periods of vulnerable/invulnerable, but those patterns are completely at odds with your central mechanic.
I think a better implementation of this idea would be if bosses took fewer hits to kill, but missed attacks would hurt you. I'd also make bosses more difficult to hit. This changes the dynamics to playing very defensively/evasively, trying to get in close to sneak single hits here and there.
The escape sequence was fun and unexpected too, though a bit too short to be worthwhile. It was over before it began!