Some (unsolicited) comments:
In context of unarmed combat, "one punch, one kill" concept is ineffective. IMHO, it is an indication of an exaggerated sense of one's ability to inflict harm with "bare hands."
Look at boxing. It is perhaps the best of the (prgramatic) pugilist systems and it does not teach "one punch, one knock-out."
Also, I would urge you not to draw lessons from movies, such as "The Seven Samurai." As much as we were all affected by cinema in one way or another, it is NOT something you should base your "life and death" training on.
The Zen concept of "Mushin" (empty-mind) is something that ancients developed from trial and error. There is a scientific basis for it.
An agitated mind results in a tense body. A tense body (especially with adrenaline) increase oxygen consumption (which means energy consumption) and gives a temporary burst of strength. Unfortunately, this is short-lived. The downsides are rapid exhaustion, narrow vision (tunnel vision), increased heart rate and inability to perform fine motor activity, not to mention inability to think, plan or act clearly.
These are all "bad" things in a fight or combat. However, they are natural phenomena that were built into us from the "caveman" days. It is extremely difficult to try to suppress them as some of them are "involuntary" (like heart rate).
The only way to suppress them is proper breath control. Breathing is the only way you can control involuntary activities of your body.
Aikido actually is quite good for learning the proper breath control (esp. the Ki Society faction). Yoga is very good as well.
For to win one hundred victories in one hundred battles is not the acme of skill. To subdue the enemy without fighting is the supreme excellence. Sun Tzu