He Said He Was Not Him

The world was once conquered by five people, but when they were all gone, the world began to become strange. Careers, guardians, rebels, all kinds of monsters and ghosts all appeared. The Four Swords once cut into pieces the protected world when no one knew about it. Navigation to the compass finally closed the sky. The guqin plays a tune on the mountain peak that no one can understand. The divine spear that punished sin turned into a devil. Have the throne and his capital fallen, and where did they fall? And who is he who lost his memory...?