Japanese schoolgirl Sakura (Higarino) has her idyllic small-town life turned inside-out when the local males start savagely killing the females. Armed with only her kyudo bow for protection and an English textbook for comfort, Sakura journeys through an apocalyptic world of mayhem.
As trauma from witnessing the violent deaths of friends and family drives her toward madness, Sakura takes refuge in an animated dreamworld where she meets Billy (Mackenzie), a character from her English text! Billy helps her survive murderous zombies, as well as an even more formidable foe in Aoi (Tsujimoto), as she races to find real-world Billy and answers to the questions: Why is all this happening? And who or what is behind it?