He was born as the eldest son of his father Yasutada, but his younger brother Yasuhira WAKISAKA was the legitimate child as he was the son of Yasutada's lawful wife, so he remained as heyazumi (an adult-age eldest son who has yet to come into his inheritance) in the beginning.
父・安董の長男として生まれたが、次弟・脇坂安坦（やすひら）が正室の子だったため嫡子となり、当初は部屋住みのままだった。