One day, a little girl moved into a room on the top floor of an old house in a certain big city. She lived with her mother, but was often alone, though not lonely, as she had many friends. Adults, however, did not see them and said she simply had a vivid imagination.

She was a strange girl.

I mean... She was a perfectly ordinary girl, but a bit strange. She called herself Little Sleepwalker so often that no one but her mother could remember what her real name was. And so it went until she finally grew up and everyone finally forgot who Little Sleepwalker was.