From the introduction: A Soul Sword is among the most potent of magic weapons, but it can be difficult to describe what it actually does. Each Soul Sword is a blank slate of the raw power of the universe, the secret runic language that describes, defines, and thus empowers every aspect of reality. When a Soul Sword comes in contact with its wielder, it’s vast reserve of undefined energy draws its form and function from the secret true runes that describe that wielder. Thus the Soul Sword of a dragonborn warlock is very different from one wielded by a dwarven cleric. In each case, the powers of the Soul Sword are drawn from the inner nature of its wielder, but the end result is very different.