with the edge of a knife, end my life

Nika becomes a witness to A.j.'s killing. he is a supernatural mercenary, killing only the lowest of the low, collecting dark hearts for his master. He should have killed her too, as the survival of his kind demands, but he isn't the heartless killer his reputation paints him to be. he lets her go, thinking it would keep her safe, outside the paranormal world. But Nika gets sucked into his world, and it is up to him to keep her safe. But when her life becomes a threat to the survival of his kind, A.j will have to weigh his heart which he can't live without: Nika or his swords..