Seiken no Katanakaji

A generation ago, an abominable war foisted a "devil's contract" upon the soldiers of countries warring on a single continent. In the middle of the legacies of that war, Cecily Campbell, a daughter of a noble house with diminished power, joined the knighthood of the free city she lives in.

One day Cecily encounters a man who dispatches some hoodlums with one sweep of a mysterious sword. The man possesses the power on the same level of the "devil's contract" that has become taboo, now that peace has been restored. Cecily has been searching for a blacksmith who can repair an old sword she inherited from her father, and that mysterious young man happens to be a grumpy blacksmith named Luke. This encounter launches their adventures together.

From the English publisher of The Sacred Blacksmith, Seven Seas:

Like her father and grandfather before her, Cecily Campbell has entered the knighthood and joined the ranks of the Knight Guards of Housman. Eager to do her heritage proud and defend her city, Cecily rushes to the marketplace to stop a madman from terrorizing the populace. She quickly realizes, however, that she is hopelessly outmatched and ill-prepared for an actual fight. A lone figure named Luke Ainsworth swoops to the rescue, a swordsman and blacksmith of much renown, who will repair the broken sword Cecily has inherited from her father and take her down a road of perilous adventure beyond her wildest dreams.