He was also a nephew of Oda Nobunaga's first wife, Nohime herself, a daughter of Saitō Dōsan.

Tatsuoki became involved in a bitter rivalry with Oda Nobunaga, and lost to him decisively in 1567.

He survived, but from this point on the Saitō clan were no longer a significant faction in the power struggles of the Sengoku period.

In one account, Tatsuoki abandoned the castle the night before the final attack, took a boat, and fled down the Sunomata River.

He lived in exile for a while,[3] but eventually sought refuge with Asakura Yoshikage.