Interesting game. I do believe the game has potential.
A couple of things I would like to note from my play through on web version:

• The lack of a life bar certainly makes things difficult, knowing how long to kill the boss.
• Another thing I noticed, is that the rage bar gets depleted on a successful attack on me
• Something weird I also noticed is that if I am not careful of how I approach the boss, I will collide with something that will push me back.
• There seems to be some weird mouse behaviour when the itch.io game is in the smaller window compared to when you make it full screen
• The attack animation is pretty slow in getting ready for the next attack, and the player has to wait for the animation to finish to launch the next attack
• The attack window seems pretty short, you would have to be incredibly close to get the hits in
• To me, the art style does not match the gameplay. You could lean more towards a cartoon-ish art style or more ps1/ps2.