Red sea urchin nigiri

Red sea urchin (Aka uni)

【Nigiri sushi: Gyoran】
What is Aka uni?
Aka uni is sea urchin caught in warm ocean areas. Its shell is 5-8 cm in diameter but the height is only 2-3 cm, giving the appearance that it has been slightly squashed. The spines are short, a full red-brown color but without the sharp tips. The spawning season is from October to November.

Since the red sea urchin (Heliocidaris crassispina), commonly known as aka uni, inhabits the same waters as the purple sea urchin (Murasaki uni), they are sometimes caught together during fishing. However, because aka uni lives at greater depths, it cannot be easily harvested by free-diving. As a result, it is available only in limited quantities and is regarded as a rare and expensive variety of sea urchin.

Furthermore, its main production areas are limited to Yura on Awaji Island in Hyogo Prefecture (famous for its “Sakate uni,” served with the underside facing up), Iki Island and Hirado in Nagasaki Prefecture, and Hagi in Yamaguchi Prefecture. Unless you dine at a high-end sushi restaurant or traditional Japanese restaurant with direct sourcing channels from these limited regions, it is quite difficult to experience this delicacy.

Its flavor is exceptionally refined, with a gentle sweetness. It differs from the rich umami typically associated with common sea urchins, offering instead a delicate and remarkably clean taste. Sushi critic Hikaru Hayakawa describes aka uni as having “a cucumber-like flavor.” Indeed, it has very little bitterness or off-flavors, and its refreshing character and pleasant finish are particularly noteworthy.

To highlight this delicate flavor, aka uni is sometimes served directly on top of the sushi rice without nori in nigiri sushi. Its flavor is distinctive enough to stand on its own without relying on the aroma of nori, allowing diners to fully appreciate its natural fragrance and lingering aftertaste.

Aka uni is a special delicacy both in terms of rarity and flavor, and it is not commonly found at sushi restaurants. However, if you ever come across it, it is definitely one of those sushi toppings worth trying at least once, regardless of the price.

Incidentally, the name “aka uni” comes from the distinctive reddish hue of its shell.

Also called Depressed sea urchin.

【Trivia】
Fresh Akauni is mainly available from Awaji Island's Yura region. This is because Kawakatsu Uni Kako, a company based in Yura, is run by a professional diver named Kawakatsu, and his son is also an expert diver. This allows them to dive to areas inaccessible to others, enabling them to harvest high-quality Akauni.

【Related contents】
Global sea urchin resources

What is uni sushi?

Why is it that sea urchin sushi can taste bitter?

List of Nimono, Gyoran and Others

(Revision date: June 25, 2026)