The Walls surrounding Tokyo is a System that isolates and encloses the city from the outside world, as well as imprisoning the Exiles from other Worlds. While the majority of Tokyo's population sees and believes that the walls are a physical structure that prevents anybody from leaving the city, the Walls' true form is a conceptual barrier. According to Ose, as long as the majority of the population believes that the walls are indestructible, that will continue to be the truth. He adds that if one wants to destroy the wall, they will need to convince everyone that it's possible to do so.
The walls are represented by the 23 Wall Dragons that embody the System of the walls, powerful beings that wield infinite power and growth, preventing anybody that comes close from crossing over. The Wall Dragons are symbolically described to be akin to an Ouroboros: a dragon eating their own tail so infinitely large that it wraps around and surrounds a whole World.