A Nanboku-cho period warrior and 9th head of the Date clan, this Date Masamune (1353-1405) shares his name with the far more famous Date Masamune (1567-1636), founder of the Sendai domain, and is distinguished by the title "Daizen no Daibu." After his father Date Muneto advanced into Okitama district and destroyed the Nagai clan in 1385, bringing the district under Date control, Masamune succeeded as clan head. In 1402, amid intensifying conflict with the Kamakura shogunate deputy, he entered Takahata Castle in Dewa Province and died there in 1405. The Date clan is said to have governed from Takahata Castle for seven generations beginning with Muneto, including Masamune, and he is honored as a "restorer of the Date clan."

A clan head who continued his father's advance into Okitama and, amid tension with the Kamakura shogunate deputy, made Takahata Castle the base of his domain administration.

He consolidated the foundations of Date rule over Okitama from Takahata Castle. His descendants later moved their base to Yonezawa Castle, and by the late Sengoku period a descendant sharing his name would become famous as the ruler of Oshu (the founder of Sendai domain). Sites traditionally identified as his grave remain in Takahata Town.