I love the idea. Having always the same boss-fight but growing stronger is super intriguing. Buuuut it does take to long for meaningful increases in your stats. I also think some more visual or tangential changes as you die would have been nice. Maybe the addition of a dodge button or so?
Also the intro sequence takes just a smidge too long for how often you have to see it.
I love the quippy dialogue but maybe it could have played while you are already in the fight instead of having to finish it first?
Furthermore I would have loved to play with wasd and other buttons than z and x especially while playing on a qwertz-keyboard.
The art is impeccable and the music is really great!