Here below is lore that was found on Acclaim's 2 Moons website. It differs from the Korean Dekaron lore a bit, but this one matches the trailer https://www.youtube.com/watch?v=zP7hx17qHyE best:
The Bagi say it was Barak, God of Battle who created the world so that he might populate it with creatures to war with one another and so honor him. The Incar say it was Karenas, The World-Bearer who thought Haran into being. This even though Trieste herself did not know how the world came to be. It did not matter, she said. What mattered was that there was Haran and there was The Abyss. One was a world of light, and the other, a dimension of darkness.
Always it is this way. In all realities, in all universes, in all beings there is that which devours and that which grows. When the world was young and unstable, wracked with earthquakes, pocked with volcanoes spewing ash and lava into the sky, drowned with constant floods, there was still life. There was no creature then to name them, but those who came after called them dragons. They ruled the water, the land, the sky. No beast could stand against them. And it was this that proved to be their downfall. The dragons multiplied unimpeded for countless centuries, each breed at war with the others until the conflict built to a war that encompassed the globe. A hundred years passed that saw the face of Haran scorched, the soil befouled, the water tainted with the blood the countless dead until only a scarce few remained.
Helion, high voice of The Old Ones, was the first to sense it – a breach, a footstep of darkness on the soil of light. Those responsible for creating a door between Haran and The Abyss were already dead, consumed by the
power they sought to wield. The Old Ones sealed the gap between the two worlds, but the damage was done. Abaddon, Lord of The Abyss, had seen the world of light. Had seen it and hated it as his black heart
had hated no other thing in existence. All The Abyss was under his dominion, and now that he’d seen there was more – more beings to devour and dominate, more souls to corrupt – he would stop at nothing to have it. And so it began, what Trieste called The Unending War.
Pitborn, the denizens of The Abyss, came to Haran by way of dark magics. Such arts had been honed in The Abyss for countless unhallowed centuries and now that the creatures who wielded such power were aware
of fresh blood and tender flesh just beyond the veil of their world, they turned their sorcery to the task. The people of Haran were strong then, schooled by The Old Ones in the ways of magic and battle. Despite their knowledge and skill, the numbers of Pitborn soon grew beyond their capacity to cope with. Though they would teach, The Old Ones would not use their power to kill the creatures swarming over Haran. Only Trieste, daughter of Helion, protested The Old Ones’ indifference. But she was bound by the will of her people and there was naught she could do.
In Heihaff, there opened a gateway to The Abyss higher and wider than the walls of the ancient cities, and beyond there came an army twisted and dark, of forms vast and vile… and leading them, Abaddon, destroyer of worlds. This would have been the end of Haran, but there are other forces in the universe besides light and darkness. As Abaddon stepped through the rift, a shimmering wall of energy appeared, stopping him and his army. It was then that The Augur revealed themselves. They are the keepers of The Balance and have no allegiance to light or darkness, good or evil – their only duty is to maintain The Balance. So many portals between the two realms had been opened that the fabric of reality itself was in danger. And this new and largest tear in space was more than the Augur could allow. They closed all gateways between the two worlds and sent Abaddon and his minions back to The Abyss.
To prevent such a thing from happening again, they decreed that only one gateway would be allowed between the two worlds, and many stayed behind to enforce their will. They remain, teleporting Pitborn and Haranian alike through what they call The Shifting Place. This one gateway, The Black Door, may hold one of three positions: closed, open to The Abyss, open to Haran. It permits a flow one way or the other, or not at all. Nevertheless, there was still some traffic between the worlds. The Summoners would not relinquish their dark arts, despite the pleading of The Incar. The Bagi were infected by an Abysmal virus that corrupted their bloodline for all time. The Segnale, Pitborn themselves, defected and were permitted passage en masse by The Augur.
The Haranians did not forget the indifference of The Old Ones in their hour of need. They turned their backs and hearts on The Old Ones. The only god to ever appear to those who worshipped him, challenged The Old Ones openly. His name was The Saint of Blades and he was a match for any of them. Only to the beauty of Trieste did he acquiesce. Helion called a council of The Old Ones and they decided that this world had seen enough use of them; they would go elsewhere and aid some other fledgling civilization. The White Lady would not leave; Trieste would not abandon her people. She had seen a coming doom. The Black Door would swing wide and the armies of The Abyss would issue forth as though a river. The Old Ones left without farewell or fanfare. One day, they were simply gone.
For fifty years, the peoples of Haran prepared for war. The Azure Order honed their bladecraft; The Incar steeped themselves in the study and practice of magic; The Summoners delved ever more deep into their black arts; The Segita harnessed the power of Haran through the tips of their arrows; The Bagi called to the far recesses of themselves for strength and pushed their twisted bodies to unknown limits; And The Segnale, the blood drinkers, assassins of The Abyss, even they gave the sternest blood of their Pitborn hearts to the ways of healing and murder.
All these long years, the most powerful of The Incar had focused the whole of their energies on holding. The Black Door shut. It was the treachery of the exiled king, Rictus, and his sorcerer, Baphomet, that undid the spells binding the door. It swung wide and the Pitborn poured through. Trieste and The Saint of Blades had developed a strategy with forces stationed throughout the land in an attempt to compensate for their inferior numbers. Though the peoples of Haran fought well and bravely, it was a futile effort and Trieste had always known that it would be. When all of the forces of each race were pushed to the frozen wastes for a final confrontation with Abaddon and his forces, Trieste disappeared. Seeing this, the others fled, all but The Saint of Blades and his followers, The White Blades. They fought to the last and The Saint of Blades, though he could not die, was beaten into a supernatural sleep by Abaddon himself.
Trieste had not fled in fear; she left in secret to seal shut the gate with an act of self-sacrifice that honored all who had died in battle. With her own heartsblood, she sealed shut the gate and the creatures of The Abyss were sucked back to their foul realm. So has it been for centuries, Haran on one side of the door, The Abyss on the other. Trieste is gone, much of the old lore is lost, the peoples of Haran are scattered and few, and now, the door opens again...
