Echo

A girl wakes up in a place she calls the Mist after knowing that she is dead.
She travels from the Mist back to the living world to try and discover more about her old life but finds nothing.
Echo then finds use out of being stuck between life and death by helping a special girl called Karasu who can appear in the Mist just like how Echo can appear in the living world. But after a traumatic life Karasu is slightly insane.