According to Kansei Choshu Shokafu, it is said that the Akai clan is descended from the Ashida clan of Seiwa-Genji (Minamoto clan), the line of MINAMOTO no Yorisue, who was a son of MINAMOTO no Yorinobu, Kawachi-Genji from Shinano Province.
赤井氏は清和源氏源頼季流（河内源氏・源頼信の子。発祥は信濃国）より発した芦田氏の流れということになっている（寛政重修諸家譜より）。