Umi budou, sea grapes in Japanese is a kind of seaweed grown and found in southwest Japan, subtropical islands of Kagoshima and Okinawa prefectures. Umi means sea and budou means grape. The official Japanese name is Kubirezuta but it is hardly recognized by ordinary Japanese.
It is a popular Okinawan dish and it can be found almost everywhere at Okinawan cuisine restaurants outside of Okinawa. However, the freshness and the quality is better to eat in Okinawa than in Tokyo.
Sea grapes are eaten as a raw, with soy sauce and rice vinegar. Then, it is consumed as a starter or garnish rather than a main dish.
Due to it is one of the seaweed which you can hardly eat in Europe, therefore if you have a chance to try Okinawan cuisine, you must order it.