The Northern Fujiwara is a family that ruled the Northeastern (Tohoku) region of Japan from the 12th to the 13th centuries, ultimately conquered by the Kanto warriors lead by Minamoto no Yoritomo. They succeeded the semi-independent Emishi families of the 11th century who were successively brought down by the Minamoto clan loyal to the Imperial throne based in Kyoto.
During the 12th Century, during the zenith of their rule, they attracted a number of artisans from Kyoto and created a magnificent capital city, Hiraizumi, in what is now Iwate prefecture. They ruled over an independent kingdom that derived its wealth from gold mining, horse trading and as middlemen in the trade in luxury items from continental Asian states and the far northern Emishi and nascent Ainu states. They were able to keep their independence vis-a-vis Kyoto by the strength of their warrior bands until they were overwhelmed by Minamoto no Yoritomo in 1189.
Soon after the Second World War, mummies were discovered in Hiraizumi (the capital city of the NorthernFujiwara), which were thought to be of people related to the Emishi who had originally submitted to Yamato rule, and hence were thought to have been related to the Ainu.
There is some doubt that the NorthernFujiwara had some Emishi blood in them, and for the most part they were part of the Japanese aristocracy.
If the NorthernFujiwara (not related to the Fujiwara of Kyoto) were related to Kyoto aristocracts the whole idea of intermarriage with local Emishi may not have been possible.