Kaguya doesn’t remember much of her past, except that she was found lost and injured, then adopted at a young age. She begins to have dreams of a boy she doesn't know, and one night he comes to her room to take her away somewhere. She is transported to a far-away word in which she learns that there are actually many earths – and soon all but the one she chooses will be destroyed.

Summary from Iskultrip Scans
Long, long ago, there lived a kami with a human face and a serpentine body, Yonagahiko, and Tetsuichi, who stood at 60 centimeters. There was a legend that surrounded the mountain where they dwelled -- that humans once slew a kami and took over..