Son of Ayukawa Kiyonaga, master of Oobasawa Castle, vassal of Uesugi Kenshin. Though descended from the same family as the Honjou Clan, the Ayukawa Clan took the side of the Uesugi family and fought the Honjou Clan when it repeatedly rose against Uesugi, though the Ayukawa Clan usually lost its battles.

In the Otate no Ran, when the Honjou Clan supported Uesugi Kagekatsu, Morinaga turned to Uesugi Kagetora, though the Ayukawa Clan lost again to the Honjou Clan. Morinaga was immediately allowed to return to serve Kagekatsu.