Tarrun is an Earth-like world with a great variety of plant and animal life. Its wildernesses remains largely untouched by humans, who here are at the bottom of the food chain and cannot afford to venture far outside their established cities. On Tarrun there is only one major landmass, so the continent is not distinguished from the planet; both are simply called "Tarrun". The oceans surrounding the continent are mostly unexplored, and thus unnamed, but the general terms North, South, East, and West are commonly used. Tarrun has a sun much like the Earth's, albeit smaller and closer, and two moons named Zaos and Aeon.

Kaiju, short for Daikaijuu, are enigmatic, giant creatures known for their great destructive power and immunity to most forms of weaponry. They vary drastically in form and temperament and are usually, though not always, one of a kind individuals with no genus, species, or evolutionary background. They exist in every corner of the globe and are always the dominant life forms in their environment. How they function and come into being is unknown, but fossil remains suggest they have inhabited Tarrun far longer than human beings.

Allinos is a thriving metropolis situated at the base of the Goronian Mountains in northwest Tarrun. Though surrounded by a desolate wasteland, many consider the city itself to be one of the most beautiful in all of Tarrun, especially at night. It has a large, growing population and a booming economy supported by trade with a number of other city-states. Its major exports are precious stones and ores mined from the mountains, as well as the mysterious substance mana, which is gathered through a non-destructive means and stored in an underground "well" beneath the city. This is by far the Allinians' most demanded resource, as it is a potent power source with almost limitless applications. Allinos itself is highly dependent on this substance, using it as fuel for many of their larger machines, such as their giant force-field generator and anti-kaiju tripod mechs. It is by use of these automated defenses that they have managed to persist past the days of their former guardians Vangar and Aphila.

Iridan is a mysterious, technologically advanced city-state located in the rugged northeast. It is surrounded on all sides (even above) by a gigantic, impenetrable wall. Essentially a city within a fortress, it is entirely indoors and cannot be seen from outside. The people who dwell there are peaceful, but powerfully antisocial. They do not allow outsiders into the city gates and rarely leave themselves; in fact, most people have never seen an Iridian in the flesh. Most communicate only by use of floating monitor screens that project their face and voice. In order to trade with other city-states they send unmanned vehicles and cargo-carrying robots across the continent. They also send support to their allies this way, transporting mana and supplies to those in need. The Iridians have never been observed participating in an actual conflict, however, and are believed to be pacifists.

Ragadin is a large, magnificent city located on the outskirts of the Gyrik Desert. It is one of the oldest settlements in Tarrun and has existed for close to five-hundred years. Many of its buildings, especially former temples and palaces, are centuries old and remain completely unchanged since their construction. Though its people take great pride in their history Ragadin is very much a modern society. Like Allinos, it attracts people from all across the globe and is actively involved in trade, being a major center for architecture, astronomy, medicine, and botany. It is often called the "Oasis City" because despite its arid location it actually has a surplus of water; an elaborate aqueduct system beneath the city supplies every home with cool drinking water and powers everything from fountains and water gardens to manmade lakes.

The Ternary Council is an intercontinental organization lead by Tarrun's three most stable city-states: Allinos, Iridan, and Ragadin. Its focus is to encourage cooperation, trade, and communication between the three powers while also looking out for the interests of their allies. It assembles twice every year, once in Allinos and once in Ragadin, to have an open forum for discussing matters of global importance. Historically it has been lead by three government officials, each representing for one of the council's cities. The current representatives are Aidan Finnbar (Allinos), Xavier Nikolai (Iridan), and Mina Lochana (Ragadin).

Kymaera Industries is a corporation well known for its exploits in gene splicing. It was originally met with fierce resistance, as the general opinion among the public was that the genetic code was not something to be tampered with. Fears of immorality and irresponsibility were voiced, but despite constant protests the company persisted and proved itself to be trustworthy. Since its inception Kymaera has produced a number of highly beneficial products including drought and insect resistant crops, cloned donor organs, and vaccines for fighting heart disease; the genetically engineered pet Tokua syntheticus is also of their design. Their work has earned them enormous respect, multiple humanitarian awards, and great financial success. Recently they have decided to expand their services by opening a wing devoted entirely to anti-kaiju technology.

Experimental Transgenetic Organism, or E.T.O., is a blanket term used to describe any living thing created by man rather than nature. Most are genetically modified plants used for agriculture, though animal E.T.O.s, like Kymaera's Toku, are occasionally created for use as pets. All are designed under strict legal guidelines, guaranteed to be genetically stable and harmless to both humans and the environment.