(This is horribly long, so I've split it into 2 posts)
BACKSTORY
In the beginning, there was the perfect darkness/chaos. One being ruled this primordial goop, and it had no had name. It created servitors, but they were eventually consumed by the roiling chaos, except a few. It was pleased with it's creations and allowed them to roam around the realm. Then the perfect utopia for this thing and it's creations came to an end.
Beings that rivaled this thing in power invaded it's realm. They called themselves 'gods'. They created something they called the 'material plane'. The thing created more servitors, and created an army to fight against these invaders. Unfortunetly, it wasn't on it's own plane anymore, and they had to become 'physical'. Whatever that was. Long story short, the thing was banished to the plane of shadow, which was all that was left of his perfect darkness. But it was forever connected to the material plane, thus being an insult to it's existance.
It's servitors were banished to wasteland planes which were created during the final battle with the thing. These things were eventually dubbed 'demons, devils, yugoloths, and youkai ' and the planes where they dwelled were the abyss, the hells, Hades, and The Makai respectively. Some of the more hideous servitors were sent to their own plane, which was dubbed 'The Far Realm'. It quickly drifted away from reality and was forgotten about. The demons and devils started a mass genocide against the other, which continues to this day. Yugoloths profited from this hatred, and became mercenaries. The Youkai stayed in the Makai and didn't worry about the politics of the other planes. All of these races remember nothing about why they were created.
The thing in the darkness tried many more times to destroy reality. Finally, after it wreaked utter carnage on an ancient multi-planed civilization (called A'tanis) and scattered it's inhabitants across the face of the mega-verse, the gods finally took a decisive action. They put an untold number of bindings on it, put it in an enchanted sleep, and cast it into a random plane. Eons passed and it awoke a few times, to direct worshippers, create Slayers (see below), and sow seeds of entropy. The most recent of these cults would be in ancient Greece, on our own planet Earth. Erebus or the 'face in the darkness' was a secretive cult, and was eventually rooted out and destroyed.
The Slayers are the favoured beings of the Shadow. These things only exist to destroy. He talks to them in their dreams, slowly manipulating his chosen to cause suffering, chaos and death. The soul slowly becomes shadow stuff, and their minds become incomprehensible. The gods hate Slayers, as do all beings that care for the material plane. When one is discovered, it is usually attacked by all forces the gods can muster; no chances should be taken. Most are whisked away just before they die, and are seen in other realms just a few years later. If all of the Slayers are assembled into an army, it will be the day the universe will be remade, but thankfully, the thing has no true plans... Yet.
Just 15 years ago, the thing awakened again, and after directing it's worshippers etc, It sensed it was close to a planet teeming with possibility. After searching for a suitable host, it entered an unborn body. Unfortunetly for the thing, the bindings kicked into overdrive and blocked out everything that it was. Eventually, with the help of 3 elite Slayers, the thing regained fragments of self. It's not complete but it's working towards it. Now if it could stop and look at the big picture, it would become a fearsome force.
(Intermission. Go get a soda, take a break, then read the rest)
THE TRIAD
Around 25 years ago, a youkai prince ran away from the court he was about to inherit. His name was Kaij. As Kaij fled his court, he ran across all that remained of a party exploring some ancient ruins that pre-dated the Youkai's inhabitation of the Makai. While he served as a bodyguard, he kept coming into conflict with the other bodyguard, a very strange man named Kuruke. Eventually the duo had to run for their lives as they awakened one of the original servitors of the thing. This demonic entity destroyed all the rest of the party and made the ruins it's home, because it couldn't leave them.
Kaij and Kuruke got into a fight, and the prince left him dead just a mile outside of the largest city on their layer; Blacktown. (the name the Youkai have given it is inpronouncable and untypable. I swear.) Kaij set up residence in Blacktown, and soon Kuruke came looking for a rematch. This time they tied and decided to put their talents to more profitable ends: Thievery. The two started out small, raiding houses and doing odd jobs. Eventually this wasn't enough for them, and they decided to try and expand their skills. Before this could happen, they were interrupted by a human.
He introduced himself as Zy and claimed to be seeking the duo that had destroyed a giant* he had been hired to kill. They explained that they had killed the giant for it's leg bone to give to a private contractor. Zy then asked if he could help them on anything that they needed done. Kaij and Kuruke didn't trust this all too eager recruit, so they sent him to 'investigate' some ruins. They knew the demon would easily tear apart this frail human and they wouldn't have to deal with him. They were wrong. Zy somehow defeated the demon (called Vell) and absorbed everything of it. This also drove him utterly insane, and he didn't recognize the fact they had sent him to die at the hands of that thing. True to their word, Kuruke and Kaij let Zy join. (if only for the fact he was insanely** powerful)
After that, something began manipulating them, speaking in their dreams. They began to kill and loot, not just loot. 4 years ago, led by Sinre, the Demon Kings banished the Triad from the Makai and sealed their powers in items. Eventually, they got back together, and were drawn to a weird lookin' kid. Zy used a spell to figure out who he was, and in doing so broke the first seal on the darkness. They know that if they release all the seals something will happen, but not exactly what.
Emmesseff has become the temporary base for these beings, and all of them enjoy it, despite what they say. But the plots of the thing are still present in the seemingly innocent MoS, and Emmesseff could just be a stepping stone on his path to reclaim his ancient throne.
*Everything can be found in the Makai.
**Haha.. That's kinda a joke.