A sheet of plain white steamed rice-flour cake, sweetened azuki beans laid across the top, cut into triangles. That is the entire construction, and what goes into the white part varies from maker to maker. In Kyoto it is eaten on one day of the year, the thirtieth of June.

That day is the summer purification rite, and it falls at the exact midpoint of the year — the last day of the sixth month, with six months gone and six to come. You eat this to get through the remaining six months without illness, which is the stated purpose and is taken reasonably seriously.

The triangle has explanations attached. One says it represents a shard of ice taken from an ice house — the ice observance was a warrior-class occasion, not something ordinary households had access to. Another says the shape is simply a square halved, standing for half a year gone.

The red of the beans is held to keep misfortune away, which is a job azuki is given all over the country. So the thing is a piece of imitation ice with a charm against bad luck on top of it, eaten immediately before the hot part of the year begins. The reasoning has largely fallen away and the date has not. At the end of June the shop windows fill with triangles.