Mu Shin means no mind. When you enter into a state of mu shin you are void of thought, you have no emotion, no expectations, or anticipation's. The idea behind this is you leave your mind and let your body do what it has been trained to do. But I think that you don't want to totally leave your mind. You still need to be aware of the situation at least on a moral and ethical level. You want to be able to stop yourself from killing or even seriously injuring your opponent if it is not nesscisarry, which depends on many things. Your skill level, the number of opponents, or whether or not he has a weapon, just to name a few.