Kiyone Sakurai, an apprentice swordmaker makes a sword for his guardian, Kozaemon Onoda. Onoda breaks the sword while defending his lord which eventually leads to his death at the hands of Naito, when Naito demands to marry his daughter Sasae. Sasae vows to avenge her father's death and pleads for Kiyone Sakurai to make a special sword for her. So Kiyone and his fellow swordmaker Kiyotsugu go to the master swordsmith Kiyohide Yamatomori to learn their craft and forge the sword.