The man and woman sit face-to-face. They lean back and support themselves with their hands on the floor. Their legs are entwined so as to achieve full penetration. All this supposedly goes on underneath the quilt that covers the low table which contains a heater.
Origin of the name
The kotatsu — a blanket-draped frame over a heat source — is said to have begun in Muromachi-era (1336–1573) Zen temples, and it remains the very symbol of the Japanese winter. In the tenements of Edo (present-day Tokyo), whole families wintered around a single one. This position tucks two people under that quilt for Kagamichausu (seated face-to-face, legs entwined), hidden from view — the 'hiding' of the name turns cramped quarters and warmth into the whole point.
Tips
Sit facing each other, lean back on your hands, and entwine your legs. Big movements are off the table, so let closeness and small rocking do the work — the snugness is the theater.
With a real kotatsu, switch the heater off or to its lowest: heat builds fast under there, so keep water within reach and surface for air often. A single blanket recreates the mood just fine.
