After introducing The Demon-God of Jubagh, I realized I should probably explain to you just how this crazy universe works. If you want the full, glorious detail, you can look at the mechanics page on the wiki, but I’ll try to give you a good overview here.
Gurhai is a finite universe. Like a geode, it has open space enclosed by an oval shell made of densely-packed organic and mineral detritus. There is a flat layer of sun systems that stretches length-wise in the very center of the shell. There are precisely one hundred worlds in the universe, separated into thirty-five sun systems; similarly, there are exactly one hundred sentient species in the universe, though not evenly distributed as one-per-world. All but two worlds in the universe are round and flat; Airdh (the First World) and Gurhai (the Last World) are the only spherical worlds, and they are at the far ends of the universe, a full year’s travel apart. The suns are mobile and small, weaving or springing between planets in their systems, and there are no actual moons. In the top and bottom halves of the void, which are striated by the layer of worlds, there are creatures unlike any found on the worlds, living on the edges of atmosphere and gravity wells.
Gravitic ore is the glue that holds the universe together; it is a polarized mineral found at the center of a planet’s crust. The polar side has a very strong attraction – gravity – and the non-polar side has a very weak attraction, but does not repel. Gravitic ore is dark and reflective, resembling a cross between hematite and coal anthracite. In addition to producing gravity, gravitic ore also produces the magical energy inherent in each world, similarly polarized; while the strength of gravity varies little between worlds, the magic density fluctuates greatly between planets, going from magic-dry to magic-rich. The polarity of the gravitic ore determines which face of a flat world will become the life-supporting side; the non-polar side will only be strong enough to keep very heavy objects in place, such as rocks and ore. The non-polar face of the world also contains dry ice, which creates the thick, drifting fog that obscures the undersides of the worlds. Gravitic ore can be carefully mined to be placed sparingly in the lowest decks of intersun ships, giving them gravity and a source of magic while they venture into the void between suns. Gravitic ore also constitutes the majority of the materials that comprise the shell of the universe, making it nigh-deadly to approach the rocky barrier; the intense gravity will pull any ships in and smash them against the rocks.
The worlds, as previously mentioned, are mostly flat, round worlds. They support life, have gravity, and produce magical energy only on one face; the other face is rocky, barren, and clouded with mist from dry ice. Worlds vary greatly in magical density, but less so in size; the smallest world is half the diameter of the largest world, and all other worlds range between them. There is a rim of high mountains encircling the entire planet, which keeps creatures, water, and other resources from falling off the edge of the world. Atmosphere is generated by the plant life on each world; it has no defined boundary, but simply gets thinner and weaker as travelers move away from the world, becoming unbreathable eventually. The skies look different on each world; in many cases, one can see the other worlds of the system, if the world faces them; other worlds appear approximately as large as Earth’s moon in the sky.
Travel between the worlds is common. A dozen races design and build their own intersun ships, but the most common by far are Loi ships, halasshian ships, human ships, and buthinian ships. Human and halasshian ships have always had gravity and a source of magical energy, due to being constructed with a very thin layer of gravitic ore in the bottom deck, which also holds the soil, water, and plant life necessary to maintain a breathable atmosphere in the void. Buthinian ships do not have gravity or magic once they leave the planet; Loi ships were the same at first, but many Loi ships are now constructed with gravitic ore in a manner similar to halasshian and human ships. Because gravitic ore is responsible for generating magic, and because magic density varies so drastically between worlds, intersun ships constructed on magic-rich worlds are more prized by most than ships constructed on magic-dry worlds. Intersun ships are shaped and built much like water-going ships, complete with a keel, multiple deck layers, an outer/upper deck, and many sails. All ships have an entire deck or more devoted to flora; once the ship leaves the planet’s atmosphere, all windows and doors are sealed, the upper deck is no longer walked, and the air produced by the plants on-ship keep the passengers alive until they reach the next planet. The universe is not an unbearably large place; fast ships can make the trip from the First World to the Last World in a year, with most sun systems having neighboring suns within a month or two of travel. It generally takes no more than a day to go between worlds in the same system.
Intersun ships do not land on-world once they have launched, since the world’s gravity would smash the vessel into the planet; the people build docks well above the world’s surface, where the pull of gravity is weaker, where the large ships can load and unload their passengers and cargo. Smaller boats without gravitic ore can make the trip between planet surface and intersun dock to transfer people and items. The hovering intersun docks are maintained via magical or mechanical means, depending on the world in question and the technology/magic level of the people who maintain the docks; the on-world boats that travel between dock and world are powered in the same fashion. Intersun ships themselves use a combination of magic, machinery, and void winds to move; the former two are what enable the ships to navigate within atmosphere or when close to worlds, but when between sun systems, the void winds propel the ships. Void winds are present everywhere near the layer of worlds in the universe, but they are not breathable by any world-dwelling creature; void winds are usually strong, can crop up into gale-force storms, and can occasionally die out and leave a ship idling in the darkness for a while.