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was a after Eien and before Shōryaku. This period spanned the years from August 988 through November 990. The reigning emperor was .
(1229–1299), was a king of the Ryūkyū Islands.
Eiso was a member of the Tenson family; and he is also known as the first of the Eiso Lineage of Ryukyuan monarchs. He served as Regent from 1235 to 1260, and afterwards as king, succeeding Gihon and reigning until his death in 1299.
Eiso's reign is generally seen as one of great growth for the fledgling Okinawan principality. Eiso instituted a variety of tax and land reforms, and the nation recovered from famines and other problems which plagued the previous reigns. Several outlying islands, including Kumejima, Kurama, and Iheya, came into the sphere of Okinawan control, and began sending tribute in 1264. An envoy was sent to Amami Ōshima in 1266, though it was not until much later that Okinawa's sphere of control would be expanded to include the Amami Islands. In short, Eiso's reign saw the establishment of many governmental institutions, and helped to set the foundation for the structure of the government of the following centuries.
Eiso's reign also saw contact with the Mongol Empire, which was at the time planning to invade Japan. Envoys from the court of Kublai Khan arrived in Okinawa twice, in 1272 and 1276, asking that the fledgling kingdom submit to the Mongols' authority and contribute to the effort to invade Japan. The envoys were rebuffed both times, and forcibly repelled the second time, though they made off with 130 Okinawan captives.
Eiso died at the age of 71, and was succeeded by his son Taisei.