So, I'd like to share our Fabula Ultima campaign that I'm playing with my friends. With me as a GM - it's my first time GMing anything ever, btw
The Papilio Realms is two large continents with some smaller islands surrounding it. Legend says, it was created by a shadow of a divine butterfly, continents are two wings. In the middle there's Heart - an impenetrable magical vortex protecting a source of magic of the world. The closer people live to the Heart, the more likely they are to have innate magic powers. If you don't, you can still learn magic, but it's hard and expensive. But if you live far from the Heart, then if you do get innate magic - it is much stronger than innate magic that people near Heart have.
Once upon a time realm was highly developed, combining technology with magic. About 200 years ago they managed to send expedition to one of two moons orbiting the world. Nobody knows what happened, but the moon exploded. After that Murk started to appear - a veil of darkness covered western wing, nobody who tried to get in could get out. And technology the world has relied upon stopped working, causing a collapse of society. A lot of knowledge was lost. In the wake of catastrophe, a new cult has appeared, they worship the Murk and call themselves Emissaries of the Moon - they are deemed heretics by Nymphalian Church, a main religion of the continent
Nowadays there are four main powers left. On the island to the north of Heart there is a Monarch Order, one of the oldest monarchies remaining, a theocracy and holy see of Nymphalian Church worshipping the divine butterfly.
On the eastern continent, closest to Heart, there's Aldanian Empire, a high magic nation. Once most powerful country, it has lost most of its dominions - but despite that it still stands strong, with Pendragon, its capital, being the biggest city in the world.
To the south there is Republic of Melitea. 35 years ago it had a revolution that replaced their monarchy with Peace Council, a parliament made up of leaders of powerful guilds. They have declared that their mission is to keep peace within and outside the country. For that reason they often hold international events, such as grand exhibitions and magical games (like olympic, but focused on magic, where mages from all over the world compete in skill)
And eastmost there's Hesperian Dominion, or Hesperia. It was a low magic country, furthest from Heart, poor and barren, and still being under economical control by Aldania. Low magic made them rediscover new way to combine magic and technology and create their own magitech, mimicking the tech of eld. And their current ruler, king Edrick Gerhard, a man born with immense innate magic, after losing his wife, has recently declared himself an Emperor and now wants to free the country from Aldania, with as much bloodshed as necessary, and then some more.
And nobody knows this, but there actually exists a parallel realm, a world on the other side of reality. It's called Tinea. It's really similar to Papilio, but it has much bigger Murk problem, and has a lot of demons. In fact, Lilith, allegedly dead wife of Edrick Gerhard, is actually a demon from Tinea Realm
But this world has its secrets that even my players don't know (and I know that it can be easily overwritten with FP use so I try to not cling on it too much)
As people live, they accumulate negative emotions, pain, loss, despair. Once they die, these emotions return to soulstream, keeping the world weak. To combat this, a couple millennia ago a highly technological civilization has built a system, that filters this negativity out of lifestream, with Murk being a byproduct of said filtration, a black fog made of pure despair.
When experienced, Murk can exacerbate negative emotions and even make self-fueled demons - i.e. demons that exist not because a lot of people believe in them (as per usual in Fabula Ultima), but because demon themselves believes strongly in its own existence: but they also make it more likely for regular demons to form.
So to get rid of Murk, a balancing system, using two moons of the world, is used to pump said Murk into Tinea Realm, leaving Papilio rich, clear and prosperous, and damaging Tinea, making it full of demons. But imperialistic wars 200 years ago really put a lot of strain on the system, with a lot of despair during the war, and a lot of people dying, making the system work in overdrive - that made the moon so frail and fragile, that moon expedition exploded it by just a slight interaction (but there may or may not be a Tinean agent in said expedition who wanted that to happen), and once one moon was exploded, balancing system broke, and a lot of Murk flowed back into Papilio
P.S. And if you noticed that it feels a bit too similar to Final Fantasy IX - no you didn't