Schoolgirl Apocalypse

Sakura is your typical Japanese school girl that lives in a small town in the mountains. One day at school, during archery practice, her teacher and classmate start acting strange. Soon, all the men in the town turn aggressive and start attacking the women. Sakura goes on the run to find the source of the problem. Along the way she meets a mother and her son, who's been infected. She gets some supplies from the mother and soon encounters another woman, but she's not so friendly. She's holding 2 people captive. The captives aren't who they seem to be. What's the real cause of the madness?