Lifespan: Eishō 7 (1510) to 11/12 of Genki 1 (1570)
Title: Governor of Shimotsuke
Clan: Akamatsu (Tatsuno-Akamatsu branch)
Lord: Uragami Munekage
Father: Akamatsu Murahide
Siblings: Masahide, Hirai Suketoshi, Kawashima Yorimura
Wife: Daughter of Akamatsu Harumasa
Children: Hirosada, Saimura Masahiro, Suketaka, daughter (an attendant of Ashikaga Yoshiaki)
Akamatsu Masahide served as a bushō and lord of Tatsuno Castle in Harima Province. Similar to his grandfather, Masahide was also called Uno Shimotsuke-no-kami.
Masahide was born the son of Akamatsu Murahide, lord of Tatsuno Castle in Harima. In 1541, Murahide died and Masahide became his successor. Masahide was known as smart and brave. He offered protection to Akamatsu Harumasa after Harumasa was driven out of Okishio Castle by Uragami Masamune who supported Harumasa’s eldest son, Akamatsu Yoshisuke. Masahide endeavored to restore the influence of the Akamatsu clan. In 1564, he killed Masamune in a surprise attack either during or on the evening of the wedding of Masamune’s son. Masahide did not have a positive relationship with the lord of his family, Yoshisuke. After Harumasa died of illness, Masahide temporarily reconciled with Yoshisuke, but then had another falling out and established his own base of support. This included a scheme to form an alliance with Oda Nobunaga and Ashikaga Yoshiaki, the fifteenth shōgun.
Masahide maintained a fierce confrontation with the Kodera clan, allies of the Uragami. He joined with Bessho Yasuharu, the head of a powerful clan in eastern Harima, to engage in battle against Kodera Masamoto and his retainer, Kuroda Mototaka. He also fought against Uragami Munekage, the younger brother of Masamune from a separate family, who attacked from the west. However, in the eleventh month of 1569, Masahide incurred a major loss after a surprise attack by Kuroda Yoshitaka, a retainer of the Kodera, resulting in the death of many of his most capable retainers. This clash is known as the Battle of Aoyama and Kawarakeyama. Having lost his capacity to resist militarily, Masahide was compelled to surrender to Munekage toward the end of 1569, losing his governance of western Harima. On 11/12 of 1570, Masahide is believed to have died from poisoning at the hands of persons directed by Munekage.