- Died: 1458
- Titles: Nakijin anji, Zakimi anji, Nakagusuku anji
- Other Names: 盛春 (Seishun, Moriharu); 毛国鼎 (Ch: Mao Guoding / J: Mô Kokutei)
- Japanese/Okinawan: 護佐丸 (Gosamaru)
Gosamaru was a lord (anji) of the gusuku (castles) of Zakimi and, later, Nakagusuku. He supported Shô Hashi, first king of the Kingdom of Ryûkyû, in his conquest of Hokuzan and unification of Okinawa Island.
Gosamaru was born in Yamada gusuku, in the village of Onna. In 1416, he led the forces of Yamada gusuku in support of Shô Hashi, king of the Okinawan kingdom of Chûzan, in his invasion and conquest of the neighboring kingdom of Hokuzan. Hashi would conquer the kingdom of Nanzan to the south several years later, uniting Okinawa Island, ending the Sanzan Period, and founding the unified Kingdom of Ryûkyû.
In recognition of his support, Gosamaru was made custodian of Hokuzan, and given Nakijin gusuku, which had until then served as the royal seat of Hokuzan. Some time later, Gosamaru left Nakijin for Zakimi, in Yomitan village, where he built a new gusuku; it is said he mobilized workers from as far away as the Amami Islands for this project, and that stones were moved by hand from Yamada gusuku to build the new castle.
For many years, Gosamaru served the kingdom loyally, and developed ties with the royal family, his daughter marrying King Shô Taikyû. Upon the wishes of the royal government, he transferred his residence to Nakagusuku, becoming the fourth lord of that castle. He engaged in construction efforts renovating or expanding that castle, and established himself there, serving to watch over another local lord, Amawari of Katsuren gusuku, who had grown powerful and wealthy from maritime trade and who had his eye on the throne. In 1458, however, Amawari reported to the royal government that it was Gosamaru who was planning a revolt, and so the kingdom's forces, led by Amawari, assaulted Nakagusuku. It is said that Gosamaru refused to fight back, out of loyalty to the kingdom, and killed himself rather than betray his loyalties and oppose his king. Amawari was executed soon afterwards, his duplicity having been reported to the throne by his own wife, Gosamaru's granddaughter Momoto Fumiagari. An alternate theory claims that the entire affair was organized by the royal government, in order to remove both Gosamaru and Amawari as powerful rivals and potential threats to the succession.
The tale of Gosamaru's betrayal and destruction by Amawari is among the more famous and popular of local historical legends. A Kumi odori dance-play telling of Gosamaru's sons' quest for revenge against Amawari, was once performed as part of the kingdom's formal entertainment of Chinese investiture envoys, and has in more recent times become a popular favorite. His grave, located a short walking distance outside of the castle grounds, is sometimes said to be the oldest extant example of kameko or "turtle back" tombs.
- "Gosamaru." Okinawa konpakuto jiten (沖縄コンパクト事典, "Okinawa Compact Encyclopedia"). Ryukyu Shimpo (琉球新報). 1 March 2003. Accessed 25 July 2009.
- "Gosamaru." Okinawa rekishi jinmei jiten (沖縄歴史人名事典, "Encyclopedia of People of Okinawan History"), Naha: Okinawa Bunka-sha, 1996. p29.
- Okinawa G8 Summit Host Preparation Council. "Three Castles, Two Lords and a Ryukyuan Opera." The Okinawa Summit 2000 Archives. Accessed 25 July 2009.
- "Gosamaru-Amawari no hen." Okinawa konpakuto jiten (沖縄コンパクト事典, "Okinawa Compact Encyclopedia"). Ryukyu Shimpo (琉球新報). 1 March 2003. Accessed 25 July 2009.
- "The Nakagusuku Castle," pamphlet available in Nakagusuku.