His childhood name, 'Fukushomaru' (meaning "vice commander" in Japanese), reflected the wish of his parents that he would someday fight enemies of the imperial court as a vice commander together with his half-brother, TAIRA no Kiyomune, who would fight as the commander in chief.
幼名の「副将丸」は、将来朝敵を討伐する際に、異母兄である平清宗を大将軍に、能宗を副将軍にという思いから名づけられた。