The grand line is a misnamed circle that marks out a 1/2 mile circle from the castle itself. It's function is so that hollows will know exactly where the law stands as far as "no fighting within a half a mile of the palace." If you are inside the circle, you are in that no kill zone. This is solely because Arancar have more important things to do than rebuilding the palace, so fighting in undesignated places inside it, or around it is forbidden. the area inside the grand line is much flatter, and the castle can generally be seen from within it.
THIS RULE DOES NOT IN ANY WAY SHAPE OR FORM APPLY TO NON HOLLOWS. IF YOU SEE A NON HOLLOW IN HUECO MUNDO, KILL IT, NO EXCEPTIONS, EVEN UP TO THE PALACE WALLS THEMSELVES.
Bleach: Rise of the Lost (Reconstructing for Reboot)
A new bleach world, with new races, and plenty of options as to where you RP