Saiin or Itsuki no In (斎院) were female relatives of the Japanese emperor (termed saiō) who served as High Priestesses in Kamo shrines.
Some Saiin became consorts of the Emperor, called Nyōgo in Japanese.
The Saiin order of priestesses existed throughout the Heian and Kamakura periods.
In The Tale of Genji, a famous work of Japanese literature, there is a story about a man named Hikaru Genji who yearned for a Saiin Princess named Asagao, but Asagao maintained a platonic relationship with Genji.
Princess Shikishi (Shikishi Naishinnō), 3rd daughter of Emperor Go-Shirikawa and Fujiwara no Seishi, was appointed High Priestess of Kamo shrine in 1159, at the age of six.