At the center of story is a teenaged girl who has been in a coma since the age of nine, when she was found with her dead parents. The mother had apparently killed the father, and then killed herself. And the girl, Aoba, was found to have her dead parents' hearts in her stomach. The core mystery, of course, is why this girl ate her parents' hearts, but there are plenty of other mysteries to chew on.
Why does the presumably imaginary dreamworld—Barbara—that Aoba now inhabits seem to affect the real world, and what is her connection to the boy, Kiriya, who she has never met and who shares her dreams of Barbara? And what does this have to do with a mysterious scientist looking for the secret to eternal youth, or, for that matter, with a long extinct race of Martians?