What is seichusen 正中線とは何か
Imagine the body to be the earth. The core of the earth is magma, this is not on the surface, but this is inside. The tanden is also inside the body. So, the seichusen is not a line in the front of the body, but the seichusen is the line inside the body, going straight through the tanden. Therefore, the seichusen changes constantly as you move around ukemi. The seichusen is a central axis.
Ishikawa sensei explaining about seichusen, Romania 2007
Changing your seichusen is an essential Wado principle, since this is a part of ‘ten I’, the change of position.
Meaning 意味
The literal meanings are seichusen: correct center line and enbusen: demonstration line. The seichusen is the center line of your own body and the center line of the opponent’s body, while the enbusen is the straight line from your seichusen to your opponent’s seichusen. Therefore in combat it is of great importance to protect your seichusen at all times. Move off the enbusen, creating a new enbusen, protect your own seichusen on the way. The new enbusen that is created should be advantageous for you and disadvantageous for the opponent. Advantageous for you and disadvantageous for the opponent are two different things.
Disadvantageous for the opponent would be such a position, that he is not able to hit you properly without having to move or correct the body. If the opponent has to move or correct his body this will be either a large connected movement or 2 movements, which is even worse. Anyway, it means that his seichusen should not be pointing towards yours.
Advantageous for you is also like the above, but there is more. Of course it is good if his seichusen is not pointing towards yours, if you stand for example at the side of your opponent, but does this mean that you are in fact in a good position? The point is, that you have to be in such a position that you can immediately hit a vital point of his body. There is only a target if this is an actual target.
To protect the seichusen is to understand all the imaginary lines from your opponent to you and vice versa.
PRINCIPLES