Yoriharu was appointed the Shugo (Military Governor) of Awa and Bingo Provinces in 1338 by the Ashikaga government and conquered the Ogasawara clan, which had served as the Shugo of these provinces during the Kamakura period.
足利氏の武家政権においては1338年に阿波国、備後国の守護となり、鎌倉時代には守護であった小笠原氏を傘下に治める。