‘A’, ‘O’, ‘U’, ‘E’, ‘I’… some things about each of them:
What you have to do is: open your mouth wide, and from the depths of your throat – and the depths of your heart – disgorge your breath and your ki… When you do this, quite naturally and spontaneously, you will utter an ‘A’ sound.
Filling yourself with the Spirit of Mizu from the sky, and filling yourself with emptiness (Mu), in a deep and guttural voice, hum an ‘A’ – and the five-row-by-ten-columns array of ancient names and wisdom: all the names and wisdom and all the possible sounds in the world… by means of – and in the form and shapes of – the sangen will circulate and be distributed and have their effect all about the Heavens. And this utterance will emerge spontaneously.
This ‘A’ sound, however and whenever it is uttered, because it is toko-tachi (forever standing), is forever the same and eternally unchanging. And for this reason, the ‘A’ phoneme is known as – with all respect –
when we she is good enough to make use of the sound of this ‘A’ phoneme, manifests herself, to effect the mending, repair and rebirth of this whole world.
– – – O’Sensei, probably audio-recorded by by Masatake Fujita, transcribed by Sadateru Arikawa Shihan, published in Aiki-Shinzui, p. 75