Uni is sea urchin commonly ate by Japanese as high grade food. The shell is spiky and the edible part of sea urchin is the reproductive grand, which is extracted from the shell. From the old days in Japan, uni has been processed with salt so it can be preserved, and has been one of the three dainty of Japanese food.
The half of the domestic production of uni in Japan is from Hokkaido. Rebun Island, where is the North of Hokkaido, holds 20% of the production of uni in Hokkaido, and the haul of uni from the island affects the market price of uni. The season of catching uni are different depending on each area of the sea. For example, in the Japan sea, the main catching season is from May to August, and in the Okhotsk sea, the main catching season is from February to May.
Uni is most of the time eaten raw, and people prefer fresh uni because it taste better than uni which is not fresh. Eating uni right away after the shell is cut open is the best timing, and there is even special uni shell opener which can easily cut open uni. The best season to get high quality uni is from spring to autumn, especially uni caught in early summer has the best quality.
Sushi using raw uni is very popular, but is one of the most expensive kind of sushi. Unidon which is bowl of rice topped with raw uni is also popular, and is said to be originated from Rebun Island. Not only uni is eaten raw, but it is also used for soup called ichigoni, which literally means strawberry stew, because the chunk of uni in the soup looks like wild strawberry. Uni is also used for pasta too.