There is a dictionary of surnames of Miyagi prefecture, but I have been unable to find it. Can someone please provide me with a proper bibliographical reference, Turabian style or the like?
The Kasai Clan in Mutsu--I can find no date more specific than 12th century for its founding. I expect it was after the fall of Oshu Fujiwara, but it would be nice to have a year. Or even a manageable range of years. .
There are few hints on Japanese Wikipedia and no specific year: Kasai Kiyoshige (葛西清重, 1168-1238) and his father defeated the Ōshu-Fujiwara in 1189. When Kiyoshige moved into Ōshu, he constructed a castle at Hiyoriyama in Ishinomaki, making it his headquarters. This could be construed as the "founding" of the Kasai clan.
So i find that Kasai was established at roughly the same time as Date (around 1189–1190). But while Date kept very good records, competition among different factions of Kasai resulted in contradictory accounts and the records of that clan are consequently quite unsatisfactory. Fortunately I do not need more than an approximate date for the foundation of the clan. There is a consensus that there were seventeen generations of clan heads, and the abolition of the clan by Hideyoshi in 1590 firm history.