The Asano are descendants of the Emperor Seiwa (850-880), of Minamoto no Yorimitsu (944-1021), and are a branch of the Toki family. Minamoto no Mitsunobu, descended from Yorimitsu in the 4th generation, settled at Toki (Mino) and took the name of that place. The Toki were hereditary shugo (Governors) of Mino province until the 16th century. The Asano name is perhaps most well known as a result of the story of the Forty-seven Ronin, whose lord was Asano Naganori, the head of a branch of the family enfeoffed at Ako (Harima Province, 53,000 koku).