Category: Hokanomono (other / roe) Season: Year round, with different varietals in season at different times. Murasaki-uni is best in the winter, while prized bafun-uni from Hokkaido is best in the summer time.
Technically not a "traditional" Edomae neta, uni is another addition to the sushi repertoire that didn't gain popularity until post WWII.
Sea urchins are encased in a spiny black shell, and the only eatable portion of the animal is its reproductive system (ovaries / gonads) which is creamy, briny and deliciously sweet. It is available year round, but summertime bafun-uni from Hokkaido is especially prized and can fetch very high prices. In the United States, it is not uncommon to be served uni from Santa Barbara, San Diego, Mendocino county (Fort Bragg), or Maine, although in my opinion nothing beats the Kyushu or Hokkaido varietals.
Often served as gunkanmaki (軍艦巻, "warship roll"), it can also be offered as nigiri-zushi, as pictured above.