From a design standpoint this is close to perfect, this shuriken mechanic where the stronger the attack, the less risk you have to take to get the enemy, is amazing. You've also got a nice variety of enemies and a clean interface. Could really benefit from some audio, at least sound effects, it would feel even more satisfying!
Also for a space game I kinda wished for a starry background but I'm just nitpicking at this point ^^