Naomasa was a noted retainer of Hatano Hideharu and held Kuroi castle in Tanba province. He was known as a capable warrior and bitterly resisted Akechi Mitsuhide's attempts to gain a foothold in Tanba. When Kuroi was finally surrounded in 1576 and sure to fall, Naomasa is said to have given into the custody of Wakizaka Yasuharu a rare sable pelt which was a family heirloom. Naomasa then committed suicide. A branch of the Akai eventually became retainers of the Todo house.