Saniwa is a person who receives shintaku (oracle) and interprets providence in religious services of Koshinto (as practiced prior to the introduction of Confucianism and Buddhism to Japan). Later, this word also came to indicate a person who plays koto (a long Japanese zither with thirteen strings) in religious service.
Saniwa' originally means 'Sayaniwa' (purified site), and the theory that Saniwa is the purified garden (site) in order to enshrine god and receive oracles is most convincing. The part of Emperor Chuai in "Kojiki," there is a description that the Emperor played koto and TAKENOUCHI no Sukune who stayed in saniwa asked for decree of god. Here, saniwa means a place, but it turned out that TAKENOUCHI no Sukune served as saniwa (a person who receives oracle). In the subsequent description, Empress Jingu was possessed by the god and gave oracle.
In "Nihonshoki" (Chronicles of Japan), it is recorded that Empress Jingu herself became a Shinto priest and let TAKEUCHI no Sukune play koto, while NAKATOMI no Ikatsuomi served as saniwa in April, 209.
Later, a person who plays Koto at Kagura (sacred music and dancing performed at shrine) came to be called 'Saniwa.'
Seiji yoryaku (examples of the politics in the Heian period), there is a description that 'saniwa is a person who plays koto and dedicates its music to the god.'
In new religious organizations in modern times and the present day, a person who reveals the true form of god and ghosts that possess people or judges their remarks of right and wrong, is called saniwa.