The Demon World (魔界, Makai; lit., "Demon Realm") is the home of all demons. It is located at the very bottom of the Universe.
The Demon World is located at the bottom of the universe and has been described as a physical plane opposite of the Mortal Plane. It is home to most of the Demon race. Similarly to the the other planes of existence, the Demon World is ruled by Kais, however, are known as Demon Supreme Kais, the evil version of the Supreme Kai.
Not much is known about the running of the Demon World except that it is ruled by a Demon King. Below him are the Demon Supreme Kais who rule over several quadrants in the realm.