Morotoki was a son of Munemasa HOJO whose name was put in the birth record as a younger half brother of Tokimune HOJO by a different father, and Morotoki's mother whose birth record is also existent was a daughter of the seventh regent Masamura HOJO.
師時は北条時宗の同母弟として出産記事のある北条宗政の子であり、母はこれもまた出産記事がある7代執権北条政村の娘。