Hidden within Kyoto is the "mirror capital" where youkai and humans live together and no one ever dies. It is protected by three people—Kurama, Yase, and Myoue—as they await the return of their parents, Myoue Jonin and Koto. One day, a young girl named Koto and her little brothers A and Un wander into the city from a different dimension looking for her mother. A mecha-geek with red eyes, it's not immediately clear whether she's human or youkai. Her arrival upsets the long peace that had ruled the city.