During the Zen Kunen no Eki (Former Nine Years' Campaign), Soen cooperated with MINAMOTO no Yoriyoshi and his son MINAMOTO no Yoriie of the Kawachi-Genji (the Minamoto clan of Kawachi Province), and received credit for subjugating the rebellion, thereby being appointed Shugoshiki (Military Governor) of Shimotsuke Province, Bettoshiki (the office of head administrator) of Ichinomiya (a shrine occupying the highest rank among the shrines of a province) of the Shimotsuke Province and Utsunomiya Zasu (titular head of the Utsunomiya Futaarayama-jinja Shrine).
前九年の役の際に河内源氏の源頼義、源義家父子に与力し、凶徒調伏などで功績を認められ、康平6年（1063年）に下野國守護職および下野國一之宮別当職、宇都宮座主となる。