Ōkubo Toshimichi
Asō is a patrilineal descendant of the Asō clan and is maternally descended from Ōkubo Toshimichi through his son Count Makino Nobuaki. Through his paternal grandmother the Hon. Kanō Natsuko, he descends from the Tachibana clan of the Miike Domain and from a cadet branch of the Ōkubo clan, who ruled the Odawara Domain.