Rusu clan

[3] They assumed the name Rusu following Minamoto no Yoritomo's conquest of northern Japan; the family, then named Isawa, were entrusted with keeping watch in the north during Yoritomo's absence (rusu (留守) being the Japanese word for "absence").

[4] In the 14th century Nanboku-chō period, the family joined the forces of Kitabatake Akiie and fought with distinction at Tsugaru and Shirakawa.

The Rusu family became established at Takamori Castle by the 16th century, and were supported by the Date clan.

The Rusu family also assumed the Date surname in the Edo period, and ruled Mizusawa, a sub-domain of Sendai.

Date Kuninori, who settled Hokkaidō in the early Meiji era, was a descendant of this clan.