This is amazing. I love how you interpreted the theme. The animations are cute, and lively. Having black and white colors is a good way to keep it simple, but also look good. I love the way the main player spins when you move.
For the sake of game design, having the player shoot automatically to kill the first enemy is a good method to convey the rules of the game without having to write anything.
I managed to kill 74 enemies before the game crashed, but it was really fun.
I could see this as a puzzle game as well. Where each level is "Kill two enemies with one bullet", but you could have some hinders, or environmental effects to help you kill the enemies for different levels. This is just a thought that I had when I started playing the game.