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From the liner notes

In the early 21st century, teenage girls between the ages of 15 and 17 begin dying all over the world. Shortly before they die, girls succumb to NDH (Near Death Happiness), a "pre-death" state of absolute bliss and joy. Once dead, a girl comes back as a flesh-eating zombie nicknamed a "Stacy".

The world is in chaos. Countries suffer from famine, war and zero-population growth because of this teenage death-epidemic. To keep the zombies from returning and eating innocent people, families are urged to kill their daughters before they are allowed to die by this mysterious disease (chopping them up and leaving them in garbage bags for government-sanctioned pick up).

In a Japanese military base, some undead schoolgirls are held and tested by a scientist who tries to unlock the secrets behind the girls' return from the dead. But the world turns upside down yet again as a soldier, in a fit of depression, lets the girls free to storm the base and devour anyone in their path...

Based on the popular Japanese novel by Kenji Otsuki. (Japanese with English subtitles)