Sanehisa had been the lord of Izumi castle in Satsuma province. He was a member of a branch family of the Shimazu. In 1526 he rebelled against Shimazu Katsuhisa and managed to expel him from Bungo Province. Sanehisa attempted to establish himself as an independent power. With the clan's allegiance divided, Iriki-in Shigetomo remained loyal to Katsuhisa and his successor Takahisa.