Since the Fujii Theory was published in the 1950s, the most popular theory states that Soun was born in the village of Ebara (modern day Ihara City) into a branch of the Ise clan residing in the Province of Bitchu, and the study of other documents has basically determined that he was a feudal lord owning half of Bitchu Ebara (worth 300 kan, a unit of rice weight used before the koku system).
1950年代に発表された藤井論文以降、伊勢氏のうちで備中国に居住した支流で、備中国荏原庄（現井原市）で生まれたという説が有力となり、その後の資料検証によって備中荏原荘の半分を領する領主（300貫といわれる）であることがほぼ確定した。