This is a great start! The challenge increases at a good pace, the variety of chasing melee and stationary projectile enemies adds some depth to the combat, and the option of increasing your power at the end of each stage adds a sense of progression. The twist of having the player fight the character they upgraded at the end is a creative use of the theme.
My suggestions for improvements would be to increase the sword swing animation speed, add some anticipation frames for the enemy attacks, and map the blocking controls to right mouse.
Keep up the good work!