One of the reasons I was originally attracted to kendo, was that as a teenage judo player I read stories of zen sword masters who could cause birds to drop from the trees with the strength of their kiai.
Over the years I have watched demonstrations of kiai jutsu first hand and of course seen the successful and not so successful demonstrations of kiai on Youtube. I of course believe that kiai is an essential part of most martial arts, but my personal jury is still out as to whether kiai can be used on its own as an effective combat method.
One thing I do know for sure, is that it is an essential part of kendo and anyone fortunate enough to have practiced with teachers of hanshi level, will agree that the strength of their ki is what makes keiko with them a completely different experience to practicing with mere mortals.
Kiai literally means the meeting of minds and can be easily understood from the advanced practice of kata. It is the mind contact that gives reason and purpose to the interaction between kendoka. Anyone watching the Kyoto Taikai or the All Japan 8th dan Championships will be aware that a lot more is going on at ki level than is evidenced through actual attacks. People sometimes compare kendo with chess, I do not agree with this analogy because where chess is cerebral, kendo is visceral.
Interestingly, although most people agree that kiai is essential to kendo, it is very seldom taught and students are left to “pick it up” as they progress. Of course the interplay between kendoka takes time and application to develop, but most beginners quickly learn to shout, men, kote, dou and tsuki.
Where there is room for creativity is in the kakegoe (the shout made before attacking). I have heard a number of interesting inventions in this area. These included unintentional cries of “sonno joi” which I believe mean “long live the Emperor, death to barbarians”. One individual whom we christened Santa, used to call out “ho ho ho” and my favourite was the Belgian kendoka who used to shout “help” through each and every keiko. The best advice is to keep it short and monosyllabic, but it is not so much the sound, as how you make it that is important.
Ideally before you move into distance, you should fill up with air and try to push it down to your abdomen. Then, when you are ready make a big strong shout, while still in safe distance. Only let out half your air, keeping the rest down in your tanden. Then make seme and only when you have committed to the attack make another big loud kiai, this time men, kote dou etc and continue shouting through your follow through and zanshin until you are back in safe distance. Perhaps it is coincidental but I find that kiai which rises in pitch tends to pull you up and helps you accelerate through zanshin, whereas kia that falls in pitch, makes you slump and slow down as you go through. The best way to practice is by prolonging your kiai in kirikaeshi, aiming to eventually do the two reps of 2 shomen, 4 yoko men forward and 5 back in one breath.
Until then “long live the Emperor and Merry Christmas”