Sunho lives in the Under World, a land of perpetual darkness. An ex-soldier, he can remember little of his life from before two years ago, when he woke up alone with only his name and his sword. Now he does odd-jobs to scrape by, until he comes across the score of a lifetime—a chest of coins for any mercenary who can hunt down a girl who wields silver light.
Meanwhile, far to the east, Ren is a cheerful and spirited acrobat traveling with her adoptive family and performing at villages. But everything changes during one of their festival performances when the village is attacked by a horrific humanlike demon. In a moment of fear and rage, Ren releases a blast of silver light—a power she has kept hidden since childhood—and kills the monster. But her efforts are not in time to prevent her adoptive family from suffering a devastating loss, or to save her beloved uncle from being grievously wounded.
Determined to save him from succumbing to the poisoned wound, Ren sets off over the mountains, where the creature came from—and from where Ren herself fled ten years ago. Her path sets her on a collision course with Sunho, but he doesn't realize she's the girl that he—and a hundred other swords-for-hire—is looking for. As the two grow closer through their travels, they come to realize that their pasts—and destinies—are far more entwined than either of them could have imagined...