Ai Genshū served as a bushō during the Azuchi-Momoyama period.  He was a member of the umamawari, or cavalry corps, of Toyotomi Hideyoshi.

The Ai were a military family dating from the Nanbokuchō period surmised to have originated as bushi in Settsu Province, later becoming kokujin, or provincial landowners.

In 1592, during the Bunroku Campaign on the Korean Peninsula, Genshū was stationed in Nagoya in Hizen Province in Kyūshū.