This was a pretty interesting idea. I beat the boss, and I really liked the music and the light effects on the boss and attacs.
It could use a bit more clarity in the tutorial, a bit of text maybe, explaining things like how you need to step into the corresponding circle to use the special ability of that element. I did have some trouble with the inverted control, you could maybe add an option to toggle it on and off.
Also, the elemental circles can be a bit hard to see if you are looking forward, you could maybe make it so the circle around the element is a different color, that way the player can tell which element a circle is even if you have your camera looking at the boss or the circle is farther away.
Overall, a nice game with a cute feel to it and an interesting exchange mechanic, good job!