A small squid is filled with uncooked rice, the opening pinned shut with a toothpick, and the whole thing simmered in soy sauce and sugar. As it cooks the rice swells and the squid contracts around it. Sliced across, each ring is packed solid with rice that has taken up the colour of the sauce.

It starts in 1941, at a shop in the town of Mori on the Hokkaido coast. The country was at war and rice was short. The problem was how to make a small amount of rice fill somebody up, and the answer used the squid that were being landed in quantity at the time. The founder's wife is credited with the idea, and the toothpick holding the opening shut has not changed since.

The logic runs the wrong way round from most stuffed dishes: the rice went inside the squid because there was not enough rice. The squid is the container and, at the same time, the thing you are eating with it.

It has since won the ranking at the national station-bento fair more times than any other item. By 2019 it had taken first place in sales fifty-one times at the department store fair in Tokyo where such things are ranked. A wartime economy measure, still outselling everything, eighty years later.