A small rice ball with a prawn tempura folded into it, the tail left sticking out, a band of nori around the bottom. That is the whole object.

Everybody assumes it is from Nagoya. It is not. It was invented in Tsu, in Mie, at a shop called Senju, at the start of the 1950s. The proprietor's wife was too busy to make her husband's lunch properly one day, so she cut up a prawn tempura and put it inside a rice ball, and that was that.

It reached Nagoya in 1981, and the manner of its arrival is worth recording. A woman who wanted to sell it there negotiated with the original couple for a month before they agreed to teach her, and the condition they attached was that she would not spread it around.

The following year a television programme in Nagoya featured it. After that a well-known comic storyteller took boxes of them around the country as gifts, the press picked it up, and the name went national. A thing handed over on the express condition that it not be publicised became, within a decade, the best-known snack of a city it did not come from. The promise broke before anything else did. Whether the couple in Tsu minded, nobody appears to have asked them.