was a local ruler of

Okinawa Island is the largest of the Okinawa Islands and the Ryukyu (''Nansei'') Islands of Japan in the Kyushu region. It is the smallest and least populated of the five main islands of Japan. The island is approximately long, an average wide, and has an ...

, who was given the title of

King of Sannan was a title given to a line of local rulers on Okinawa Island from the late 14th century to the early 15th century. Contemporary sources on the Kings of Sannan are scarce and mutually conflicting. The narratives on the kings have gradually been ex ...

. He first contacted the Chinese emperor in 1403, claiming himself to be a younger brother or cousin of Shōsatto, the late King of Sannan, who reportedly had no son. Ōōso was given the title in the next year. His last contact was of 1413. In 1415,

Taromai , read variously as Tarumoi and Tarumī, was a local ruler of Okinawa Island, who was given the title of King of Sannan. He first contacted the Chinese emperor in 1415, claiming himself to be an heir to King Ōōso, without clearly specifying his b ...

, who styled himself Crown Prince, reported Ōōso's death. He claimed that Ōōso was killed by his elder brother Tabuchi, who had in turn been killed by local chiefs, in favor of Crown Prince Taromai. His real name is unknown. The name ''Ōōso'' is enigmatic and highly un-Okinawan. A desperate attempt of decipherment relates it to Yaese (八重瀬), a fortress in southern Okinawa. Historian Ikuta Shigeru speculates that the King of Sannan was a puppet of the King of Chūzan from the very beginning. According to his theory, Ōōso reported to the Chinese emperor that King Shōsatto had no son because Shōsatto and his offsprings actually defected to Korea in 1398. Before the recognition by the Chinese emperor, Ōōso was appointed as King of Sannan by the King of Chūzan. Similarly, historian Wada Hisanori suspects that Ōōso was not a younger brother or cousin of King Shōsatto and that it was a made-up story to eliminate Chinese suspicion. Based on the assumption that by that time,

Shō Hashi was the last King of Chūzan and the first king of the Ryukyu Kingdom, uniting the three polities of Chūzan, Hokuzan, and Nanzan by conquest and ending the Sanzan period. Family * Father: Shishō * mother: daughter of Miiko * Wife: sister of I ...

, the unifier of Okinawa Island, had already kept Sannan under his control, Wada claims that Ōōso was either a pseudonym of Shō Hashi or his puppet ruler. The ''

Chūzan Seikan , compiled in 1650 by Shō Shōken, is the first official history of the Ryūkyū Kingdom. In six scrolls, the main text occupies five and an accompanying summary the sixth. Unlike later official histories such as ''Chūzan Seifu'' and ''Kyūyō'' ...

'' (1650) and

Sai Taku , also known by his Japanese-style name , was a Ryukyuan aristocrat and bureaucrat in the royal government of the Ryūkyū Kingdom. Sai Taku was born in Kumemura on January 4, 1645. He descended from Cai Xiang. He took part in the compilation of ...

's edition of the ''

Chūzan Seifu was an official history of the Ryūkyū Kingdom compiled between 1697 and 1701 by a group of scholar-officials led by Sai Taku. It was a Kanbun translated version of ''Chūzan Seikan''. Later, it was rewritten into Classical Chinese by Sai Tak ...

'' (1701) made no mention of Ōōso, suggesting that the name of Ōōso was not transmitted among the Okinawan society.

Sai On (1682–1762), or Cai Wen in Chinese, also known as , was a scholar-bureaucrat official of the Ryūkyū Kingdom, serving as regent, instructor, and advisor to King Shō Kei. He is renowned for the many reforms he initiated and oversaw, and is amon ...

's edition of the ''Chūzan Seifu'' (1725) drastically rewrote history. Having access to Chinese diplomatic records, he added the records of tributary missions sent under the name of Ōōso. Sai On dated Ōōso's death to 1414.

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{{authority control Kings of Sannan