Sagami's dates are unknown, but she was probably born around 1000. Her real name was Oto-jijū. Her paternal ancestry is unknown, but she was supposedly a daughter of Minamoto no Yorimitsu. The fourteenth-century work Chokusen Sakusha Burui claims Yorimitsu was her father, but the Kin'yōshū includes a renga by Yorimitsu and "Sagami's mother", so it is also possible he was her adoptive father. Her mother was a daughter of Yoshishige no Yasuaki, governor of Noto.