I like the idea of the game and also the art. I definitely see a lot of potential here, but here are some small tweaks that might end up making your game much much better!
- maybe add an option to run backwards because if you miss a ninja, you can't complete the level
- increase the hit range on the ninja because right now you have to be really close to attack
- be able to attack the enemy ninja stars and CANCEL(destroy) them, I think this feature would be SUPER nice and make the gameplay feel much more interesting
So yeah I think you have a good game here that could be made much better with some small changes. Good job man!