The origin of the Yoshimine clan goes back to YOSHIMINE no Yasuyo, who was the son of Emperor Kanmu, demoted from nobility to subject, therefore Sosei was a great-grandchild of Emperor Kanmu.
良岑氏は桓武天皇の子で臣籍降下した良岑安世にはじまり、素性は桓武天皇の曾孫にあたる。