Origem: Wikipédia, a enciclopédia livre.
- Kerr, George H. (1965). Okinawa, the History of an Island People. Rutland, Vermont: C.E. Tuttle Co. OCLC 39242121
- Kerr, George. (2000). Okinawa: The History of an Island People, p. 52 , p. 52, no Google Livros; although the paramount leaders of Okinawa beginning with Shunten (c. 1166 – c. 1237) are commonly identified as "kings," Kerr observes that "it is misleading to attribute full-fledged 'kingship' to an Okinawan chief in these early centuries... distinctly individual leadership exercised through force of personality or preeminent skill in arms or political shrewdness was only slowly replaced by formal institutions of government — laws and ceremonies — supported and strengthened by a developing respect for the royal office."
- Nussbaum, Louis-Frédéric. (2002). Japan Encyclopedia, p. 172, p. 172, no Google Livros; excerpt, Eisō [with a macron] was "king of the Ryūkyū Islands in the thirteenth century."