Shinjōsaimon-in was born on October 12, 1653, Japan. Her name was Fusako Fujiwara. Her father was Takatsukasa Norihira, who had the post of sadaijin and the junior first rank. Her half-siblings by other mothers included the kampaku Takatsukasa Fusasuke, the sadaijin Kujō Kaneharu, and Takatsukasa Nobuko, the wife of Tokugawa Tsunayoshi. Another theory holds that Fusako was actually Norihira's younger sister, whom he adopted as his daughter.