In May 1576, Naomasa went to the front at the siege of the Ishiyama Hongan-ji Temple (Ishiyama War) along with Mitsuhide AKECHI, Murashige ARAKI and Yusai HOSOKAWA and took charge of the capture of Mitsu-tera Temple, but was ambushed by the soldiers of Hongan-ji Temple and died in a melee.
天正4年（1576年）4月、明智光秀、荒木村重、細川幽斎らとともに石山本願寺攻め（石山合戦）に出陣し、主力として三津寺攻略を担当したが、本願寺側の伏兵に遭い乱戦の中討死した。