The Demon Sword Asperides

For two centuries, the demon sword Asperides has guarded the body of an evil sorcerer while much of its consciousness takes a break from its former work. That work involved persuading humans to wield the sword, with their souls as the cost. Nack Furnival has trained from birth to become a brave, noble knight, though he is not very good at it. Asperides and Nack then set out on a quest to save the world.