Kyousougiga.

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 (same name, different spelling) 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.