Kyousougiga (2013)

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 also 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 is not immediately clear whether she is human or youkai. Her arrival upsets the long peace that had ruled the city.