Kago no Naka no Alicis

Long ago a central tree gave life to an entire world. When it began to wither, a girl wept before it until her love revived it. She was named Alicis and locked in a cage as a living conduit for the tree. In time she fell in love with a man and gave her love to him instead. The tree began to fail again. They fled the cage and entered a different world, where a blinding light killed her. The man's grief curdled into a hatred of all light, and he covered the world in darkness. In the present, a girl named Sumeragi Runa has a recurring dream of a withering tree. On her way to school she hears a voice and is pulled into a parallel world called Luche by its two guardians, M and L. A red-haired man named Harvey appears to collect her at their request, and brings her to a castle called Sefira, where she meets the Roacrysto.