Andō Masasue served as a bushō during the Sengoku period. Masasue served as the fourth head of the Hiyama branch of the Andō.
The Andō were a gōzoku, or wealthy family, with a presence in Dewa and Mutsu provinces, along with the lands of the Ezo peoples (comprised of Hokkaidō (excluding lands in the Matsumae domain), Sakhalin Islands, and the Kuril Islands).
The Andō clan originated from the environs of Tosaminato in Tsugaru in Mutsu Province, a gōzoku with operations in ocean transport to facilitate trade with the peoples of the Ezo territories. In the era of Andō Morisue, the first head of the Hiyama branch of the Andō, he had his younger brother form a cadet family and expanded his power to the Akita District of Dewa. Andō Yasusue, the second head of the Hiyama branch, wielded his authority based upon recognition from Emperor Gohanazono as the Shōgun of Oushū-Tosaminato (Tosaminato of Mutsu Province). Yasusue’s son, Andō Yoshisue, was killed in action during a battle against the Nanbu clan resulting in the end of the Shimonokuni as a lineal branch of the Andō.
The details are uncertain, but Morosue, the son of Andō Shigesue (who, in turn, was the son of Morisue’s younger brother, Ushiogata Shirō Michisada) called himself Yoshisue’s adopted son and immediately set about to revitalize the Shimonokuni family. The Nanbu clan granted him landholdings on the Shimokita Peninsula and he adopted the surname of Andō, serving as a puppet of the Nanbu. He governed the Andō family distributed across lands in the area of the northern oceans, contributing to stability and efforts by the Muromachi bakufu to assert its authority in the region.
In 1454, after losing in battle against the Nanbu clan, he crossed with Takeda Nobuhiro to the Ezo lands within the sphere of influence of the Shimonokuni family. He then harbored with Kakizaki Sueshige, the lord of the Hanazawa house in Kaminokuni, his son-in-law and servant of the family. Nobuhiro later married Morosue’s daughter after her adoption by Sueshige. (According to another theory, she was the daughter of Iemasa.)
In 1456, Morosue nominated Sueshige as the military governor of Kaminokuni, Andō Iemasa (Morosue’s younger brother and the lord of the Mobetsu house) as the military governor of Shimonokuni, and Andō Sadasue as the military governor of Matsumae. He then responded to a solicitation from Andō Koresue (a member of a cadet family and the lord of Akita Castle, the base of the provincial governor of Dewa having the title of Akitajō-no-suke) and moved to Shōroku Island. Before long, he decimated Kasai Hidekiyo of the Akita-Kahoku area (later known as the Hiyama District) and constructed Hiyama Castle to serve as his main base.
Thereafter, he aimed to recover Tsugaru from the Nanbu clan. After receiving one of the characters from the name of Ashikaga Yoshimasa, the eighth shōgun of the Muromachi bakufu, and changed his name from Morosue to Masasue, endeavoring to expand his power. On 9/15 of Chōkyō 2 (1488), a retainer named Osagi Yamato launched a rebellion at Kahoku-Nukano Castle after which Masasue took his own life.