The Ouchi clan claimed descent from Crown Prince Imson, son of King Seong of the Baejje kingdom in Korea; indigenous to Suo Province, they became warriors in Japanese society, and reached the rank of gokenin (lower-ranking vassal) under the Kamakura bakufu (Japanese feudal government headed by a shogun).
大内氏は百済聖明王の皇子琳聖太子を祖と称し、周防国に土着して武士となり、鎌倉幕府の御家人に連なった。