What is "saiin"

were female relatives of the Japanese emperor (termed saiō) who served as High Priestesses in Kamo Shrine. Saiō also served at Ise Shrine. Saiin princesses were usually elected from royalty (内親王, naishinnō) or princess (女王, joō). In principle, Saiin remained unmarried, but there were exceptions. Some Saiin became consorts of the Emperor, called Nyōgo in Japanese. The Saiin order of priestesses existed throughout the Heian and Kamakura periods.

Saiin is also the name given to the palace where the Saiin Priestesses lived and served the Shinto deities.