Very interesting concept, I thought it was a bit confusing. I had to check the game page to know that you should press J to attack. If there's more than one enemy on screen, the enemies won't die, their health bar just decrease until the minimum and then they won't take any more damage. There must be a bug when checking their death condition. Also, I don't really understand if I should try to kill all enemies or to die, the goal isn't clear.
I liked the physics based strick with the red "sword". I hope you continue developping it!