He was a son of Sai Kôso, who had served as music instructor for two earlier Edo missions, in 1748 and 1752. Two of Ninki's elder brothers, Sai Ninchô and Sai Ninhô, were notable instructors of Chinese music as well, and served together in training musicians for a 1772 mission to Kagoshima. Unlike most such instructors, Sai Ninki had never traveled to China; however, he was still able to secure such a position, as a result of his education and expertise coming from such a family.
His kafu (official genealogy) indicates that he was appointed to this position on 1795/3/23, and taught until 1796/5. That same month, on 5/2, members of the mission performed before the king; having received his approval that their preparation was sufficient, they departed Ryûkyû on 7/13.
- Liao Zhenpei 廖真珮, "Ryûkyû kyûtei ni okeru Chûgoku kei ongaku no ensô to denshô" 琉球宮廷における中国系音楽の演奏と伝承, in Uzagaku no fukugen ni mukete 御座楽の復元に向けて, Naha, Okinawa: Uzagaku fukugen ensô kenkyûkai 御座楽復元演奏研究会 (2007), 111-112, citing Naha shishi 那覇市史, vol 6 上, Naha City Office (1980), p328-329.
- Itaya Tôru 板谷徹, “Kafu ni mirareru geinô shiryô 2: Edo nobori” 家譜に見られる芸能史料, Musa ムーサ 9 (2008), 174.