Diddu (pronounced /ˈdɪduː/) is a godworld of the Sacred Sea, notable for the radical transformations that the world and its contents undergo between its sixteen mesters. The people of Diddu have, however, established some locations, the Golden Cities, that are protected from the mestral alterations, though anyone leaving the cities is subject to the changes as usual. By no means all Diddu's inhabitants live within the cities, however, and those who do not are as subject to the transformations as anything else in the world.
Diddu is shaped roughly like three spheres, connected by narrow necks of land. Various protrusions project from each of the spheres. All the spheres are inhabited, though one, the Dark Sphere, is considered notably more dangerous than the other two. A patchwork of water and land covers the world, with the land covering approximately 38% of the surface. The largest settlement on Diddu is Qalardin, one of the Golden Cities; outside Qalardin, the largest settlement is the port city of Harambare, on the shore of the Harvage Sea.
Diddu's day is only marginally shorter than Earth's; exactly four hundred Didduan days make up the year. The year is divided into sixteen periods called mesters, varying in length but averaging twenty-five days. During each mester, the world and its contents undergo a drastic transformation. One mester, for example, sees the world covered in water—except the former seas, which become underwater expanses of air—; another sees the world's surface submerged in a thick layer of gel. In another, the world becomes frigid and glacial; in yet another, it becomes warm and extremely fertile.
While the mesters are sufficiently fundamental to life on Diddu to make up an important unit of the calendar in virtually all cultures, there is some variation in precisely where to draw the line between mesters, and which mester to start the year with (and, of course, in the names they give the mesters). The nowaday most widely used calendar, called the cubic calendar for somewhat obscure historical reasons, begins with Jiricin, the mester generally considered to be the baseline of normality from which conditions in other mesters deviate. The full sequence of mesters in the cubic calendar, with their length in days (according to the most common reckoning), is as follows:
- Jiricin, 32 days
- Gandagabian, 19 days
- Canoan, 21 days
- Bajiber, 29 days
- Gurunda, 27 days
- Bukoan, 25 days
- Fansinda, 22 days
- Lulean, 26 days
- Calian, 30 days
- Hauau, 21 days
- Worohue, 23 days
- Derean, 31 days
- Nunean, 20 days
- Farinda, 27 days
- Ienoan, 24 days
- Jijian, 23 days
For the most part, conditions in each mester are quite different, but there is an exception: two mesters which, though there may be subtle differences, have matching in their most notable characteristics. These two mesters, Gurunda and Derean—sometimes collectively called the Bunanj or the Mortal Mesters—, are also the mesters most dreaded by most of the world's inhabitants (though Canoan may not be too far behind). During these mesters, most of Diddu's mortal inhabitants are temporarily turned to metal statues, while undead roam the world in their place.
There is also some cultural variation in the numbering of the years, even within the cubic calendar. Different societies have counted from the foundation of various empires or other significant events, but in more recent years—thanks to the influence of the prophetic angels Senelda, Œldon, Kalt, and Moraia three thousand years ago—the years are generally numbered counting down toward a supposed future event—while the angels' prophecies may not be widely believed in, this reverse year numbering still remains as a relic of it. The current year by this numbering is 1321.
Diddu is inhabited by a variety of species, though the dominant intelligent species is the human. Because of Diddu's mestral transformations, however, exactly what species exist varies by mester—some creatures only exist at all during certain mesters, while others change into other creatures. During two of the mesters, for example, all humans (and other living creatures) become frozen metal statues while the world is haunted by undead, while in another certain plants become animate that throughout the rest of the year are unmoving.
In addition to the void magic common throughout most of the cosmos of Loge, Diddu is home to several arcana of its own, the most notable being the steel magic that seems tied to different metals. Like everything else about the world, though, magic seems to work differently during different mesters, void magic being somewhat less susceptible to change than most other forms.