Visually the game looks great and incredibly polished!
I really like the concept behind the shuriken mechanic too. It might be embarrassing for me to admit, but I couldn't get past the first boss. I'm sorry that I didn't get to see the other bosses, I really tried. I just thought that the boss was way too tanky. As far the shuriken mechanic goes, I believe it could have been handled a bit differently, for example, clicking or holding left mouse to keep throwing the shuriken and holding right mouse to throw and place it and then release it for the charge. Unless I was close to the boss, my shuriken would just get stuck in place, but if I got too close I didn't have enough time to dodge the projectiles that spawned. I also think that you should keep iframes for a second or two after the charge, because most of my charges ended up with me just getting hit.
My skill issue aside, this game is very well made! Great job!