Zombies took over the Tokyo area.

The people lived without hope in underground shelters.
The girl Hisako who grew up underground was told the word school by her grandmother.
School is a place where children play and learn. It is a paradise for young people. The best place to spend your youth.
Hisako dreamed of school and one day she is sitting on a subway train going up above ground. What awaits her there? Despair...