i really love this concept! my only suggestions would be to give some sort of indication about where the hatchet is going to go before release. i might just be bad at the game but it felt a little random to me (i did beat it though! not the secret boss, but just the main 3!)
i think what maybe could make it feel a little better would also be letting the player use either LMB or space to charge up the spin? i found it hard to maneuver/jump while charging because my left hand was doing all the work.
i'm looking forward to playing this in its finished state!! very good job so far imo