The Rusu of Mutsu province were descended from Fujiwara Kaneie (929-999) and adopted the Rusu name following Minamoto Yoritomo's conquest of northern Japan in the wake of the 12th Century Gempei War. During the Nambokucho Period they supported the Southern Court and joined the army of Kitabatake Akiie. They entered the Sengoku Period established at Takamori Castle and connected with the Date family. The Date provided them with a number of heirs, and the Rusu had essentially become a related retainer family by the late-16th Century.
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005