Pretty fun little game. The art is beautiful and the core gameplay loop is addicting,
Some feedback: It got pretty impossible to charge superpower later in the game when the ninja is moving faster. It reaches this point pretty quickly, too, so by the time I learned how to play the core game it was too late to charge superpower, which is a real shame because it's a cool mechanic with some sweet visuals. Maybe tweaking the charge conditions to make it easier to charge superpower or making the ninja accelerate more slowly would fix this problem. Also, the "0" keybind for superpower is a little awkward to use without a numpad, maybe consider a keybind that is more friendly for smaller keyboards.
Nice work on this game!