Katanagatari.

The legendary swordsmith Kiki Shikizaki created 1,000 swords in his career. The more of the swords a country owns, the higher its chances are at winning a war. When the shogun emerged victorious, he collected 988 swords, but these were merely the “practice pieces”. The last twelve swords were the crowning achievements of Kiki’s career. Each one of them is so powerful that a single man could defeat an army with it. Togame, the shogun’s strategist, gets the order to collect these swords. At first she hired a ninja, but each of the swords’ value is so high that the entire ninja clan went rogue once they got hold of one. She then put her trust in another warrior, but he kept the sword for himself. Her final hope now is Shichika, the seventh and last student of the Kyotoryuu School.