Inspired by Celestial Maidens from Korean myth and pitched as Final Fantasy meets Castle in the Sky, an amnesiac sword-for-hire and a theatre troupe performer with mysterious powers discover that their destinies will change the fate of multiple worlds.

Seventeen-year-old mercenary 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 in the slums 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 coveted mithril for any assassin who can hunt down a girl who wields silver light.

Meanwhile, far to the west, sixteen-year-old Ren is a cheerful and spirited theatre troupe performer living in an idyllic mountain village with her adoptive family. But everything changes during one of their festival performances when the village is attacked by a horrific humanlike monster with sharp claws and teeth. In a moment of fear and rage, Ren releases a powerful silver light she didn't know she possessed, killing the monster - but not in time to save her foster father's life, or to stop her adoptive brother from being grievously wounded.

Determined to save her brother from succumbing to the poison inflicted by the monster, Ren sets off over the mountains to the east, 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 assassins) 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 . . .