Originally, the highest position of kokushi was kokushu, but when kokushu did not live in his assigned province, a person at the rank of suke, jo or sakan (these ranks were in this order, with suke the highest) was appointed to zuryo.
本来、国司の最高職は国守だったが、遥任により現地に在住しなかった場合は、介・掾・目のうちから受領が出ていたのである。