Shoun was the son of FUJIWARA no Tadanari of the Miko Hidari family and the nephew of Kaishu who held the position of Tendai Zasu (the highest post of Tendai sect).
昌雲は御子左家（みこひだりけ）の藤原忠成の子であり、天台座主（天台宗最高の地位）を務めた快修の甥にあたる。