In 874, he and his father relinquished their imperial descent and became commoners, taking the surname "Taira" and descending to subject status; Sadafumi took a position as deputy commander of the Palace Guard of the Left, Jugoinojo (Junior Fifth Rank, Upper Grade) post.
874年（貞観_(日本)16年）父とともに平姓を賜って臣籍に下り、従五位上左兵衛佐に至る。