Saya Otonashi ought to be just another teenage girl in school except that she remembers nothing of her life before the last year or so. All she’s sure of is her family: her adoptive Vietnam-veteran father, George, and her two brothers, Kai and Riku. They live in Okinawa, not far from an American airbase, where the jets and bombers scream overhead and a mysterious long-haired man in the park plays the cello in a way that seems hauntingly familiar.

“Who am I?” Saya asks herself, and it isn’t long before she gets the first and most brutal clues towards answering that mystery. One night she sneaks back into school to retrieve a pair of shoes and is assaulted by a “chiropteran” — a monster that once was human, and now feeds on the blood of humans to survive. She’s almost mauled to death by the creature, but then the cello-player shows up, infuses Saya with his blood to revive her, and gives her a sword. When infused with her blood, she can use it to kill these creatures … and kill she does, much to her own shock and dismay.