I used to teach this a long time ago. But then I sensed that people could not really understand or grasp it. Anyway, here it is again, the three variations to applying sak-ki “force of the killer” as taught to me in the ninja dojo back in the 1970s:
Sak-ki – Experiencing and projecting a state of intending to do harm to your adversary. When you can project sak-ki, you can summon up an invisible barrier around you. People can sense the danger and they are “creeped out” and unconsciously move away from you. This perception of sak-ki is tested in the To-Shin Do 5th degree test, where I strike down at your head or shoulders from behind with a shinai practice sword.
Sei-ki – Once you have become familiar with subconsciously picking up sak-ki cues from people projecting it, you can sense when an adversary is bluffing or is deadly serious. He might be smiling and nodding, but you sense his hidden desire to attack you. He may be huffing and posturing, but you sense that he is unsure and hesitant to carry out an actual attack. You can train to react. Based on what you sense, you can adapt and position yourself to respond effectively.
Mu-ki – You can develop the ability to hide your sak-ki killer intent. You bide your time, clear your mind, observe minutely, respond naturally, and then suddenly attack without any preplanning in your mind. Your body gives off no detectable subconscious cues. Mu-ki gives you the ability to interact with people in an outwardly humble, courteous, and agreeable way. However, with the flip of an internal switch, you explode into sak-ki.