In the gorinto, the five ring stupa raised across Japanese Buddhist grounds since the Heian period, Ku, void, caps the structure as its fifth and topmost tier: a jewel or flame shaped finial set above Fu's crescent, differing in kind from the four solids beneath it just as the element itself is said to differ from the four material elements it sits above. In the bodily mapping used in Shingon meditation on the gorinto, Ku corresponds to the crown, the point where the individual form opens onto what the tradition holds to be beyond form altogether.
No fixed shape captures Ku as directly as the cube, sphere, triangle and crescent capture the four beneath it, and ritual visualisation of its seed syllable is correspondingly described as an opening toward emptiness rather than a concrete image, consistent with Ku's identification with the sky, spirit and creative potential rather than a material substance.
Miyamoto Musashi closed his seventeenth century Book of Five Rings with a Void chapter shorter than the rest, using it not to add a fifth technique but to describe the state beyond technique, where a master acts without conscious calculation, a reading of Ku as the culmination the other four elements build toward rather than one more category alongside them.