According to Mato and Insane black rock shooter, This is black rock shooter's world. However, she is never shown to actually reside here. The world is a wide, empty space with some ruins embedded in the floor. The ground has the typical checkerboard pattern of most locations in the other world, but with a bluish tint. The entire battlefield seems to be surrounded by a black-blue rocky material that prevents those inside it from seeing the outside world. The battlefield resembles a cavern or a large hall. Unlike most of the other battlefields. It is practically empty except for some large. Spiky objects stuck in the ground.
5 parts