Become a Demon Against Mortals, Become an Immortal Against Devil

One day, the mortal family was assassinated to death by the immortal's plan. Later, his heart seemed to turn black, as if he had awakened some power, as if he had always been just a pawn in the immortal's hands. Later, he met his childhood sweetheart. In order to protect her, he was willing to give up his own life and take her away. Later, they became close to each other and relied on each other. For the last time, they finally survived this calamity, as if it was a test before, and they finally became immortals.