I had a lot of fun with this one! The ninja theme is great and I liked the fast pace of it.
On Gamepad, the menus worked but I couldn't move my character at all with the d-pad or the joystick (8BitDo SN30Pro controller). It worked fine on Keyboard though.
Interface is intuitive. I would have liked an exclamation point "!" appearing over the Shop button in the main menu whenever I have enough money to afford something new.
The katana weapon seems weak; it has a limited range and the animation lasts longer than the actual hitbox. As far as new weapons you could add, how about bamboo that juts up from the ground? Some sort of boomerang weapon that comes back to you could be cool (though not sure how to make it ninja-themed).
As others have pointed out, level three is a huge difficulty spike, and even with max shop upgrades, I struggled to kill even one single enemy.
But I like the concept. Leaning into the theme and adding some shrines around the map where you can get buffs for the run would help this game stand out.