15 years have passed since modern civilization ceased to exist due to an incredible disaster.
A certain part of society has been able to adapt, and literally lock themselves in a city, where children grow up and are educated to survive. However, they are unaware of what happened, they are even used to living behind an immense wall.
Meanwhile, outside of what seems to be a paradise, life is very different, people die of hunger, or are eaten by strange creatures.
In paradise, a girl named Tokio begins to question her life, and one of her friends, Mimihime, seems to predict some situations in her future, starting that day as they face a surprise test in class.
During the exam, Tokio receives a strange message on her tablet, and is asked if she would like to see the outside world, beyond the wall.
Outside, we meet Maru, a boy with advanced self-defense skills, who travels with Kiruko, an older girl, who is supposed to take care of Maru while she looks for a doctor and a friend.
In general, the cities have been devastated, and there is little property that has not been looted by the survivors. The boys decide to enter a house, only to find a couple who lost their lives due to starvation.
When they attempt to cross the city, they are intercepted by some adults, who threaten to rip them off if they don’t leave their belongings, but Maru and Kiruko end up defeating them thanks to a strange weapon that she has.
Days later, the youngsters arrive at what appears to be a hotel, exchange information and goods with the owner, but when both boys tell her that they can fight one of the man-eating creatures, the owner is put on alert.
Later, after a bath, they receive food and go to sleep immediately, apparently receiving some kind of drug that renders them unconscious before the monster appears on the scene.
Back in paradise, Tokio can’t sleep, after all, earlier, Mimihime told her that she dreamed that two people were looking for the city, and that a boy is the exact copy of her friend.
Tokio goes for a walk and finds some adults, and the most important person in the group decides to confess that it is true, beyond the wall there is a bigger world, but in total chaos.