He often feuded with the members of a main branch of the family Taneuji SOMA, Morotane SOMA (not Shigetane's father) and others over territory and he left for Mutsu Province to build Kodaka-jo Castle to expand his power that led to form the foundation of Mutsu Soma clan.
嫡流（下総相馬氏）の相馬胤氏や相馬師胤（重胤の父とは別人）らと所領を巡りたびたび争いをおこし、陸奥に下向し、小高城を築くなど勢力を広げ、陸奥相馬氏の祖となった。