Daggerbound by T. Kingfisher

Four hundred years ago, three warriors were trapped inside enchanted swords, cursed to be immortal servants of whoever wielded the blade. One of them is the Dervish, a restless, fiery soul who hates his captivity and hates his wielders even more, but has never found a way to escape the sword's magic. Then one day, a disillusioned scholar named Learned Edmund is tasked with delivering the sword to a distant city, and, in the greatest of peril, draws the blade. The Dervish finds himself bound to a sweet, brilliant, and above all kind young man. And while he may be able to protect Edmund from bandits, cultists, dragons, and strange inhuman diplomats, he may find it much harder to protect his own heart. Paperback / 442 Pages