At this time, the male heir of the Hojo family was Tomotoki HOJO, who was Yasutoki's younger half-brother by father's lawful wife; however, Tomotoki fell from power because he had aroused the anger of Sanetomo MINAMOTO, the third shogun, and therefore Yasutoki, who was a son of his father's mistress, became the male heir.
この時点で北条氏の嫡男は異母弟で正室の子である北条朝時であったが、朝時が第3代将軍・源実朝の怒りを買って失脚したため、庶子であった泰時が嫡男とされた。