All the martial arts have their own cry or “kiai”, which is often quite terrifying.
This is apparently the expression of the sudden release of energy from the body. A romantic interpretation of the kiai has made it famous in the West under the name “cry that kills”. In actual fact the kiai is a setting up of wave lengths’ between two contestants. He who has the greatest amount of subtle energy “ki” makes it known by the kiai.
It is undeniable that, just for a fraction of a second, a sort of inhibition occurs, just long enough to strike the opponent. It is also said that by the kiai some masters are able to paralyse a bird on a branch, to make it fall at their feet even. In this case, the technique used is to make the kiai the vehicle for a sort of hypnotic energy, just sufficient to immobilise the bird for a brief moment.
The kiai must come from the stomach, that is from the centre of true energy; if it comes only from the throat, it is ineffective: in this case, nothing more than a guttural sound is emitted. The kiai, is the art or science of using ki or energy.
The expression ‘vital energy force’, or subtle power within things, means that all forms of life, especially budo, are an application of this energy. ‘Vibration existed both at the beginning and at the end; between the two, the earth and the universe have lived’. On this ancient Shinto thought, rests a profound esoteric understanding. The vibration (impersonal state of energy) is seen as a sound in the mind (specific state of energy). To know the power of sound is to make energy vibrate, in other words to make life itself vibrate.
All things can be explained by sound or rather by the vibration modes of sound. This ancient knowledge, fully confirmed since by numeric scientific applications (power of sound over plants and animals in particular) enables one to understand how the kiai can be so much more than a blood thirsty cry and can express its energy in all areas of existence. In this case, the kiai can also be silent; above all it implies an active decision from the mind, such that the strongest uses his influence over the weakest.
The kiai is controlled by the hara, or what the Japanese call fukushiki kokyu, in other words deep breathing from the stomach. Breathing exercises train one to do this.
The kiai is definitely the result of a science which embodies a command of breathing, as well as of the mind. The spirit controls ki which makes the hara vibrate. The kiai in a way projects mental, physical and psychical energy. That is why the word KIAI is the opposite of AIKI.