Kokū is considered one of the three fundamental honkyoku. This piece exists in different schools and is associated to different legends. Here are some of them, for inspiration. Source: The International Shakuhachi Society.
Kokū, Kyorei and Mukaiji are the three oldest songs (Koden Sankyoku) for shakuhachi. There are at least half-a-dozen different transmissions of this song from various temples and sects in Japan. Fudaiji Koku is played in order to experience the boundaries of mu. Mu is often translated as “nothingness”, but in reality is the illusionary aspects of various phenomena of existence “there” or “not there”, “still” or “moving”, “alive” or “dead”, etc.
Vacuity. This piece is considered as one of the most ancient in the repertoire for shakuhachi. Its title identifies it as a musical evocation of Sunyata (Vacuity). As he plays, the musician tries to attain a state of selfless detachment where he is no longer enslaved by this material world, although not yet liberated from it, and he strives to merge with the universal consciousness. This shows how much the artists playing shakuhachi were committed, through music, to their quest for spirituality.
Kokū (Empty Sky) Legend has it that Kyochiku, a founding monk of the Myoan-ji temple in Kyoto climbed Asama mountain and spent the night there. In a mystical dream he heard this melody. Koku is one of the three most important Honkyoku along with the pieces Mukai-ji (misty ocean bell) and Kyorei (Empty Bell).
Kokū means “Empty Space,” or “Empty Sky,” and evokes the feeling of Fuke-Zenji’s bell ringing in the empty sky. (“Ko,” “empty”, and “Ku” “space, or sky”.) This piece is also known as Koku-ji; “Ji” is an old Chinese word for a wind instrument, but now generally just means instrument, so the piece is usually just called Koku.
Like Mukaiji, this piece was supposedly heard in a dream by the 12th century priest Kyochiku. The image in this dream is like that of Mukaiji; of floating in a boat, with the mist blocking the moon, and the sound of the flute coming from the empty sky.
Koku has a flavor of infinite mist and echoes. It is said that playing this piece helps one explore the boundaries of “mu” or nothingness, transcending reifications, the artificial cognitive boxes into which we place objects, situations and emotions. Jin Nyodo wrote that if it is played in a very penetrating manner, “All delusion will fade away and a quiet spirit – a fusion with the great void or the Koku (the bell ringing in the empty sky) will arise.”
The special story behind Koku, “Bell Ringing in an Empty Sky,” has already been related. Fuke-Zenji’s prediction of his own death and subsequent disappearance from his coffin, and the sound of his bell coming from the sky made the sound of his bell especially meaningful. The attempt to recall this sound is the basis of Koku.
Koku starts with three tsu-re’s, like the sounds of a bell ringing. There are rather long pauses between each, and each repetition is slightly fainter and not as long. These tsu-re’s are symbolic of the overtones that FukeZenji’s bell would have made. When you ring a bell, you hear the waves of its overtone vibrations long after the initial sound.
After playing the first tsu-re, the sound of a bell like Daibosatsu’s temple bell reverberated back from the empty sky across this large lake because of a natural echo from the surrounding mountains across the water. It was quite evocative of the original story of the sound of a bell coming from the empty sky. There was just enough time between these notes, as we are taught to play them, to allow echoes of the sounds to become an integral part of the experience.
Our version in the Hijiri-ryū (Sainte-Ecole) is close to the Taizan-Ha version.
Here is a practice recording on shakuhachi 2.4: