Grilled canned pork and a thin sheet of fried egg, folded into rice and nori so the whole thing closes over on itself. Okinawa shortens the name to potama. Cut across, it shows a band of pink beside a band of yellow.

The canned pork arrived during the American administration after the war and settled into households as an ordinary ingredient, and the reason it settled so completely is not a happy one. Okinawa's pig farming had been destroyed in the fighting. There was no fresh pork. Canned meat kept without refrigeration, so it stood in for what was gone.

Fried pork alongside an egg dish became a set meal on the menus of ordinary canteens, listed simply as pork tamago. The rice ball is a compression of that plate into something you can hold, and it is said to predate onigirazu, the folded rice sandwich it resembles.

Now it is stacked in supermarkets and convenience stores across the islands, sold in canteens, and made by dedicated shops, one of which opened in 2014 and where the fillings run past twenty kinds. A substitute for something that no longer existed became what a great many people here eat before work, standing up, on the way to somewhere else.