WORLD

OverviewTerminologies
Jail

Jail - the living prison

The Jail is an organism that suddenly appeared, causing a sinkhole in the middle of the city.
It created a giant prison 666 meters beneath the surface, with the surrounding walls so steep and perilous that it is impossible for the people to climb out.
As a living prison, there is a tower in the center of the Jail that seems to be growing. Could this be humanity's only hope of escape? 　 　

Areas within the Jail

The Jail created multiple areas resembling prisons, and each area is said to house something called a "core."
Each area housing these cores is protected by a great abomination known as a "Nightmare."
Blood Maidens
A rare group of girls who were born in the Jail. They possess physical prowess beyond the capacity of normal human beings, and employ a variety of special powers.

These girls all have names from old stories and folk tales, but the reasoning behind it is a mystery...

Hameln Liberated District
The base of operations where Otsuu and Little Mermaid, as well as Mamoru's group, operates from. It was formerly some kind of subway, and was where Hameln called home. Because of this, Hameln calls the place "Hameln Liberated District," but it didn't seem to catch on with others.