The Backyard is an alternate world in Guilty Gear. It is said to contain all the information that creates the real world. It is also an encapsulating term that refers to the source of limitless energy known as Magic. It is the codex or source of transferred information that comprises most of the world as physical manifested data; the source of what makes the real world exist. The world itself is said to be a virtual space, resulted from the information conveyed from the Backyard. Upon entry to the Backyard, the extremely restricted data pressure is immense and anyone who enters must be "tuned" to the frequency the Backyard emits in order not to be crushed by the dense information contained within it. That Man is known to have kept and constructed the "Cube" within this location.
The existence of the Backyard is first revealed in Guilty Gear 2: Overture, when Sol Badguy visited Dr. Paradigm in Ganymede. Youkai like Izuna and Valentine with her Vizuel army were born from the dimension.
The Backyard is described as being "similar to the relationship between a game and the computer" according to Daisuke Ishiwatari, and said to be like a book containing the theory of the world, essentially being the equivalent of the Akashic Records within the Guilty Gear Universe. The mechanical process of producing a reality is created by various factors. Anything that happens in the real world cannot affect the Backyard; however, certain elements within the Backyard can apply and change this world's existence. Various places, like the Underworld (Guilty Gear: Judgment), act as parts and "layers" of the Backyard, and by definition, those beings that live within the various levels connected to the Backyard or within the Backyard itself that are not artificially constructed are called "Youkai". Demons, monsters, mushi, mutants, ghosts, Guardian Spirits, and deities are implied to be those creatures. The Original Man was the first human to have ever entered the Backyard and come back alive. Following this, he comprised all of his knowledge of the Backyard into a book known as the Sage's Testament.