In the gorinto, the five ring stupa built across Japanese Buddhist grounds since the Heian period, Ka, fire, is carved as the third tier: a pyramid or triangular form set above the sphere of Sui, its point aimed upward in visual contrast to water's roundness and earth's flat base. In the bodily mapping used in Shingon meditation on the gorinto, the triangle of Ka corresponds to the region of the chest and solar plexus, the seat of the heat and drive the element is said to carry.
The seed syllable associated with Ka is chanted and visualised on that triangular form, part of a ritual sequence in which the five syllables in order are held to unite the practitioner's body with the layered cosmos the stupa depicts, distinct from the gorinto's everyday role as a grave monument raised over the dead.
Miyamoto Musashi's Book of Five Rings gives its Fire chapter to combat itself, the direct clash of forces, timing and the decisive strike, a martial application of the same transformative, consuming energy Ka carries in ritual contexts, where fire is the element that converts an offering, or a body, from one state into another. Musashi treats the Fire chapter as the book's core, the point where strategy meets an opponent rather than principle alone, and he draws it out at greater length than any of the other four.
The pairing of a devouring, upward form with the mid position in the gorinto's five tiers also echoes fire's older role in Vedic and Buddhist ritual more broadly, as the element that carries an offering from the human realm to a higher one, a transformative function the gorinto's own funerary purpose, marking a passage from life to whatever lies beyond it, quietly reflects.
Sources The Symbolism of the StupaAdrian Snodgrass with A Book of Five RingsMiyamoto Musashi, translated by Victor Harris