Neighborhood

The Neighborhood (近界(ネイバーフッド)), also referred to as Neighbor World (近界民(ネイバー)の世界), is the world on the opposite side where Neighbors and Trion Soldiers come from, including Yūma Kuga.

Each country travels across the sea of darkness on their own orbits, like stars. Yūgo Kuga called this existence "Planet Nation" (惑星国家). Their movements are a bit different from those of planets orbiting the sun, but many of planet nations brush by human world while revolving closer and farther. Every planet runs on a star (which itself is a Trigger). The star must be kept fueled, or it will die, and the land would eventually crumble. Only when they're close to human world, they can send out their away ship and open a Gate to carry out an invasion. Many planet nations don't have fixed orbits and fly around freely in the Neighborhood. These have been called "Errant Nations" (乱星国家).

Geography
There are currently 9 known nations:
 * Calvaria: A defense nation which was at war with Spinthir.
 * Spinthir: A nation which was at war with Calvaria.
 * Menoeides: The nation which the Expedition Force, consisting of Tachikawa, Fuyushima and Kazama Units, departed from in the Black Trigger Retrieval Arc.
 * Liberi: The maritime nation surrounded by a rich, vast sea.
 * Leoforio: The cavalry nation where battles are fought on special Trion Soldiers.
 * Chion: The snow country where harsh terrain and climate thwart enemies from attacking.
 * Aftokrator: The god's country and the largest military state.
 * Galopoula: A vassal state of Aftokrator.
 * Rodochroun: A vassal state of Aftokrator.
 * Ergates: A nation from which Xeno and Lilith come.