Harumune was eldest son and eventual heir of Date Tanemune who succeeded to power following a feud with him that lasted for over half a decade and is remembered as the Tenbun no ran. After securing his positon, Harumune had moved his headquarters to Yonezawa castle, and this became the Date capital. His time as daimyô was spent working to reestablish the influence of the Date, which had been considerably eroded by his conflict with his father. He came to disagree with his son Terumune on various matters but rather than risk a repeat of the Tenbun no ran he retired. He died on 12 January 1578.
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005