SAKKI is "advanced" and also "basic" at the same time, and we refer back to it at certain points, including my own experiences of both the Test and actual combat
Here is an interesting piece with Hatsumi Soke speaking about it:
During a later training season, one of the students asked Soke in a polite tone: "What do all these personality aspects has to do with fighting?"
Hatsumi sensei smiled warmly.
"They have to do with not needing to fight".
There was a momentary pause while we contemplated the comment.
"There are certain types of conflict where you might not even realize that you have an adversary. You would not even have a chance to fight.
How do you fight a sniper armed with a silenced rifle? How do you fight an assassin who stabs you unseen from behind? How do you fight the man who
rigs your car to explode when you turn on the ignition?"
The teachers present kept their gaze on the master. They seemed to know the answers. The rest of us shifted around uneasily and looked at each other
with questioning glances.
Hatsumi sensei broke the silence.
"There is no way that you can fight him."
It was not the answer I had been hoping to hear.
"Since you cannot successfully fight this adversary, you must learn to protect yourself in other ways. The ninja refines his perceptive abilities
to a level higher than most humans, and becomes sensitive to input from sources in addition to his five physical senses. The ability to perceive what
we call 'premonitions of danger' takes the ninja to the fifth of the nine developmental levels.
"An attacker, whether man or animal, puts forth his harmful intentions as a sort of vibration or thought impulse. Just as we say that sights, smells,
or sounds are things, we can also say that thoughts are things. The ninja refers to these thoughts impulses that accompany harmful intentions as sakki
(the force of the killer). This sakki is there to be perceived, regardless of whether or not we are sensitive enough to pick it up.
"When you are sensitive enough to detect this intention of harmful action, you can fight back by simply not being where the attack will take place."
