Aoyama Nobumasa served as a retainer of Oda Nobuhide and guardian of Oda Nobunaga. He is also known under the name of Yosōemon.
In 1542, Oda Nobuhide (Nobunaga’s father) assigned Nagoya Castle to Nobunaga. Nobumasa was one of four elders appointed by Nobuhide to raise and educate Nobunaga. In addition to Nobumasa, the other three elders included Hirate Masahide, Hayashi Hidesada, and Naitō Shōsuke.
In 1547, Nobumasa departed for the front in an assault on Inabayama Castle in Mino. While the forces were en route, Saitō Dōsan launched a surprise attack, known as the Battle of Kanōguchi. Nobumasa and many other Oda forces were killed, including Oda Nobuyasu, Nobunaga’s uncle and lord of Inuyama Castle. There is an alternate view that Nobumasa died in an earlier battle in 1544. In that case, Nobumasa would have died prior to Nobunaga’s coming-of-age ceremony.
Nobumasa’s son, Aoyama Yoshitsugu, served Maeda Toshiie, a sengoku daimyō of Noto Province who served Oda Nobunaga and Toyotomi Hideyoshi. Yoshitsugu also served as deputy of Uozu Castle in Etchū Province after Sassa Narimasa captured the castle in 1583 from Suda Mitsuchika, a retainer of Uesugi Kenshin.