Female Knight of Death from Another World

He was once ordinary, but this ordinaryness could never return to him, because he became her, with different bodies holding the same memory. Her body was gone but was brought back to life as a death knight. Light is not necessarily a partner, but darkness may support each other. When fate allows her to meet 'them', how will the death knight choose? In a world where strength means everything, she has an identity that is not recognized by the world and tries to find her true self. The death knight possesses more than just killing, darkness, plague, lost souls and the rune sword...