Rusu Kagemune served as a bushō during the Sengoku period.  He was the sixteenth head of the Rusu clan.

The Rusu originated from the lineage of Fujiwara no Michikane of the Fujiwara Hokke in the Heian period.  During the Sengoku period, the clan was based at Iwakiri Castle situated on Mount Takamori in the environs of Sendai in Mutsu Province.  Iwakiri was in a strategic location near the intersection of the Nanakita River and a major road in Mutsu known as the oku-no-taidō.  This gave rise to an assemblage of markets comprising the largest commercial district in the Tōhoku Region.

In 1492, Kagemune was born as the second son of Date Hisamune, the thirteenth head of the Date clan.  Rusu Kunimune, the fifteenth head of the Rusu clan, lost his eldest son and designated heir, so Kagemune was adopted as his son-in-law and successor.  In 1495, after the death of Kunimune, Kagemune inherited the headship of the clan.  In 1506, he defeated the Kokubun clan in a battle at Kozuru.

From 1542 to 1548, Date Tanemune, a sengoku daimyō and the fourteenth head of the Date clan, engaged in a protracted struggle against his eldest son, Date Harumune, for control of the Date clan.  This is known as the Tenbun Conflict.  During this event, Kagemune cooperated with Harumune by fighting against the Kokubun clan who supported Tanemune (Kagemune’s older brother).

In 1554, Kagemune died and was succeeded by his eldest son and designated heir, Rusu Akimune.