Setting: (Note: I'm taking great liberties with real-world mythology, here.)
The world looks like the world we know. However, Ragnarok (the mythological End Times War) is real. The Aesir, ancient supernatural beings of immense power, once known to the Norse people and other cultures as gods, have been waging this war for centuries against their enemies, the Vanir. The Aesir have managed to imprison the Vanir's great leader, Loki, but his consort, Hel, is working hard to release him in order to bring about the Last Battle. If Loki wins, he will destroy the world and create a new one under his rule.
The Aesir utilize the power of Light (good magic), while the Vanir wield the power of Shadow (evil magic). These two forces coexist in the world. According to legend, it was actually the Vanir who taught the Aesir how to use magic, in the first place. A key aspect of magical power is the use of ley lines. As has always been speculated, ley lines are energy channels for Light and where they meet you get a white nexus. Shadow has similar channels, called hollisch lines, and two or more hollisch lines cross at a black nexus. Supernatural beings can use the channels to travel from place to place and can boost their powers by accessing the wells of power at the heart of a nexus.
To help them in their fight, the Aesir and Vanir each enlist the aid of mortals. Some mortals make pacts with these beings through which they gain the ability to shape the forces of magic and are called Arcanists. Additionally, those whose faith and will are strong enough gain the title of Acolyte and may channel the forces of Light or Shadow directly. Additionally, there are heroic and villainous people who know about Ragnarok and are fighting with more mundane means on either side either to defend the world or in the hope of claiming a piece of the new world that Loki will create if his forces win the war.
The Aesir have gathered together their greatest warriors and formed the Schattenjaegeren. These “Shadow Hunters” are elite soldiers in the fight against Hel’s minions. Whether they wield magic or mundane weapons, these men and women stand against the Sceaduhund, the “Shadow Hounds,” and their cohorts.
There are other beings in the world, created by the raw magical energies of the universe, but these beings are rare. Additionally, as Ragnarok escalated, the immortals drew upon more and more of the power of the nexuses in the world. Since only an unclaimed nexus can spawn Light or Shadow creatures, the random occurrences of these beasts has decreased over time.
Recently, mankind has become vaguely aware of another kind of power in the world: Twilight magic. This power, coming from the very force of mental power and of life itself, can only be wielded by mortals. Along with the discovery of that energy came the discovery of the channels through which it has moved for millennia. Since very few people have walked these lines before, they became known as “Untredan,” or untrod, lines. Their crossroads are known simply as Grey Nexuses. It is entirely likely that this new source of power, held firmly in the hands of mortal beings, will change the very course of Ragnarok. If mankind claims its right to decide its own destiny, the event that Richard Wagner called the “Twilight of the Gods” may have more than one meaning.