Fallen Dreams: Echoes from the Black (Fantasy RPs/ World Building)

I am currently working back into top writing form, and am engaging in some world building for fantasy. While this may be a bit ambitious, I am thinking of something like FoG's Emmoria project on a smaller scale, and would like one or two partners to collaborate with to help finish the general world basics. I already have a general idea of one area and how it works, including basic magic rules, a few religions, a couple governments, and some general history. My idea is not to create a set of individual worlds connected together, but rather a more general and unified world like forgotten realms, or war hammer.

If no one is really interested in world building, I do have an immediate idea for a thread. It is based around a vaguely mysterious and long forgotten foe awakening in the Far North. The only kingdom that has a chance of stopping it before it begins a new catastrophic war is Sellas, an ancient and extremely powerful kingdom. Sellas has already suffered a probative force and suffered for it. A few of Sellas' best manage to drive it off but suffered a horrible tragedy. Gensial, the king's eldest son, sacrificed his soul to seal away the Dark and buy his three compatriots time to make the kingdom ready for war. However, the death of Linna has driven the three best of them apart. Belius was driven mad with grief and set off to the east to master the forbidden dark arts of Necromancy. Arcturus became obsessed with domination and power, seeking it as a method to prevent that loss again. Turien sought relief through religion.

Now, ten years later, Gensial's great soul is withering, becoming tattered under the unrelenting assault of the Dark. Small forces leak through the seal and raid the surrounding areas. Despite warnings from the ranger battalions in the north, Sellas is in no position to respond in force. Two of empires on both the southeast and southwest borders are agitating against each other, and applying unsubtle diplomatic pressure for a war-time alliance. Necromancy and grief has driven Belius insane. He lurks in the graveyards of a fallen empire to the east, controlling his conquests with a bony fist. Arcturus has united the fractious Kythians (like the Norse and Danes during the height when they went a-viking) that pirate the coasts and seas to the northeast, and lusts for yet more power. During this unstable time, anything might be possible. Will you stand against the Mysterious Dark or attempt to seize power under one of the factions?