Aoyagi Seian served as a bushō during the Azuchi-Momoyama and early Edo periods.
Seian was born as the lineal heir of Aoyagi Yorinaga.
The Aoyagi were members of the Omi clan of Shinano Province. In the era of his grandfather, Aoyagi Kiyonaga, the family was granted by Takeda Harunobu (later known as Takeda Shingen) the Omi township in the Tsukama District and, thereafter, adopted the Omi surname.
After the demise of the Kai-Takeda clan in the third month of 1582, his father, Yorinaga, obeyed Ogasawara Sadayoshi. Owing to suspicions of collusion via Sanada Masayuki with Uesugi Kagekatsu, as well as efforts to curse Sadayoshi, he was invited to Fukashi Castle and then murdered inside. His base at Aoyagi Castle was then seized by the Ogasawara army. Details thereafter are uncertain, but it appears he served the Sanada clan.
Seian became a retainer of the Sanada clan. In 1600, at the Battle of Sekigahara, he joined the Western Army and was defeated. Sanada Masayuki and Sanada Nobushige (Yukimura), father and son, were banished to Kudoyama. Among the sixteen people who accompanied Masayuki to Kudoyama, Seian was one of a few, along with Nobushige, who entered Ōsaka Castle. After the death of Masayuki, other retainers returned to Ueda while Seian joined Takanashi Naiki and remained at the command of Nobushige at Kudoyama. Later, he deployed for the Siege of Ōsaka. In 1615, during the Summer Campaign of the Siege of Ōsaka, it appears that Seian and Nobushige were killed in action.