 His clan, originally the , was of uncertain origins.According to later Tsugaru clan records, the clan was descended from the noble Fujiwara clan and had an accent claim to ownership of the Tsugaru region on the Tsugaru Peninsula and the area surrounding Mount Iwaki in the northwestern corner of Mutsu Province; however, according to the records of their rivals, the Nanbu clan, clan progenitor Ōura Tamenobu was born as either Nanbu Tamenobu or Kuji Tamenobu, from a minor branch house of the Nanbu and was driven from the clan due to discord with his elder brother.In any event, the Ōura were hereditary under the Nanbu clan's local magistrate Ishikawa Takanobu; however, in 1571 Tamenobu attacked and killed Ishikawa and began taking the Nanbu clan's castles in the Tsugaru region one after another.