Central Questions
1. What are the nature and history of the three planes, mana, elements, gods, demons, and devils?
2. What do gods/demons/devils do? Want? Why? Restrictions? Rules? Limits?
3. Why did gods build dungeons and form the System?
4. Why do gods allow or design dungeon fights?
5. Who killed Dorn's parents and why? How?
6. What did Dorn do for his first 2,000 years of life?
7. What does Dorn know about the Demon and Devil Plane, demons, and devils?
8. What does he plan to do? What does his ultimate goal look like?
9. What's the history behind the dwarves, elves, humans, beast-kin, and other monsters/beasts?
10. What're the details of Kiera's story, involving her parents, her younger brother, and the noble?
11. How did Kiera's parents get a cultivation style book?
12. What's Emelia's story?
13. What's Ravenlord's story?
14. What's the Hartjenstein family's story? How did they become so bigoted?
15. What's the drow's story?
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Partial Answer for Questions 1-5
Before there was the Universe of Three Planes, there was nothing. No planes, no space, no time, no energy, no matter, no mana. Nothing.
An interesting interaction can be ovserved with the combination of matter and anti-matter (matter existing with the opposite polarity, where electrons are + and protons are –). When the two types of matter interact, they violently explode, completely annihilating both, and releasing vast amounts of energy. Interestingly, this process can also happen in reverse. A vast amount of energy inputted into nothingness can give rise to both matter and anti-matter.
Similarly, a vast amount of energy injected into nothingness (known as origin energy) can create two types, or poles, of mana, that exist in complete and eternal opposition. This pair of mana types can be called mana and anti-mana, + and –, A and B, 0 and 1, or even Celestial and Infernal. As for the presence of the origin energy, it can be attributed to an old universe obliterating via natural processes or some type of supernatural, immortal existence ending itself. The way is unimportant; all that matters is that nothingness and vast energy, from somewhere, combined to form these two types of mana in the region of reality now known as the Universe of Three Planes.
Due to the input of energy into the existence of such a system, both mana types are physically attracted to each other, like the bonds of gravity between matter or the electrostatic attraction of + and – charges; this mana attraction is a form of potential energy. Reality 'wishes' for the two types of mana to reunite, releasing the potential energy held in between and relieving the stress that their existence and separation gives rise to. Without the intervention of other forces in such a system, a reuniting is exactly what would occur, leading to the complete destruction of both types of mana and a return to nothingness, possibly even the resurrection of the old universe or the supernatural being.
In the face of impending destruction, both mana types gave rise to primitive intelligences. These two 'primordial' manas, despite instinctually wishing to converge and destroy each other, instead used their energy to move further and further apart, their intelligence driving them towards survival. However, no matter how far they separated, with only nothingness in between and no new outside forces, they were simply delaying an ending, fighting a losing battle. In the end, both manas would expend themselves, another way of returning to nothingness.
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In a remarkable bout of symmetry, both manas decided to stop moving apart from each other, and instead, they built a plane of existence to surround themselves, like a fortress. The two primordial manas separated small parts of their own energy to create new lifeforms and bestow intelligence, giving rise to the first gods and demons (devils are different and came later). Both of these new beings were creatures of pure mana, given intelligence. They were created in the image of their makers. With the two fortresses built and the suboordinates created, what remained of the primordial manas became the kings of the two planes of existence. Each king still represented more than 99% of the total mana present in each plane, however. And then the kings sent the forces to war, attempting to destroy each other's new plane and forces.
Predictably, equal losses on both sides mounted up quickly, achieving nothing. With identical pasts, strengths, homes, and forces, it was impossible for one side to gain an advantage. After this second stalemate, the two kings finally came together (but always with a small distance, for obvious reasons) to form a peace treaty, hoping to begin enjoying their own existence instead of fighting for it. As for the gods and demons they had created, it was decided that the two kings would co-create a different, unique, and new means of competition, one that wouldn't be damaging to themselves. The demon king and god king believed that with such a method, the war could end, and instead of focusing on destroying each other, they too could become invested in and amused by a new, competitive pastime. It was seen as an ideal way of passing eternity for immortal and un-changing beings of pure mana.
Together, the demon king and god king each separated another small part of their energy (still <0.01%). By combining the two in a controlled way, a plane of matter and a plane of anti-matter were formed. They decided to collectively name these two planes, the Lower Planes. They observed these new, matter and anti-matter based planes. There were trillions and trillions of planets and stars in each, but now, they were stumped on how to form a competition. Knowing that only life was capable of competition, they decided to see if they could form a new, matter or anti-matter based form of life through experimentation.
Still, they believed that even a new matter or anti-matter based life would require mana, for mana was all that they knew. Working together in the interest of a fair competition, they eventually managed to find a way to mix their two manas together in a homogenous fashion, creating a new, pure mana. But it was unstable. Thinking of how to fix this, the god king tried binding an infinitesimal piece of this pure mana to a small piece of matter, a rock, from the matter plane. Thus was born the first dungeon core, an intelligent being made of rock. After creating it, the god king noticed that it was physically attracted towards the anti-matter plane. After consulting with the demon king, the god king tried chucking the rock onto a planet in the anti-matter plane. They watched, enthralled, as the dungeon core began absorbing anti-matter and emitting pure mana into the planet, propegating pure mana on its own. And it was expanding quickly!
Noticing an extraordinarily minute imbalance between the two planes forming, the devil king quickly bound a tiny piece of pure mana to a rock made of anti-matter, before tossing it onto a planet in the matter plane. It acted exactly in the same way, emitting pure mana into the matter plane. The two kings grinned at each other, in discovery. They didn't know what would happen, exactly, but they started creating more and more dungeon cores, tossing them on tons and tons of different planets. But always in equal amounts between both planes. The Lower Planes began filling up with mana. Matter interacted with pure mana as well as the forces of gravity, electromagnetism, and the strong and weak nuclear forces, and new lifeforms started being created. Quickly, even intelligent matter or anti-matter based lifeforms appeared. Then, these creatures started absorbing tiny amounts of pure mana, storing it in their matter or anti-matter bodies. The two kings watched, amazed, as the beings used this absorbed mana to form all sorts of different elemental magics, doing many different magical things, and they grew excited watching how the fights and wars between races became more and more fantastical.
The stage was finally set. Quickly, the two kings agreed upon a set of rules for their new competition. The gods would take control over the matter plane, including the matter dungeons residing in the anti-matter plane. Likewise, the demons would take control over the anti-matter plane, including the anti-matter dungeons in the matter plane. The goal was to try to destroy the other's plane, using only the dungeons. Next, they hammered out a system for the competing dungeons to grow more powerful and destroy more matter or anti-matter, more quickly. They called it the System. The gods and demons would reward and limit their dungeons with growth abilities for liberating matter/anti-matter and killing matter/anti-matter based lifeforms. Once a year, each dungeon at or above a certain power ranking in the matter plane would fight to the death against dungeons at or above the same power ranking in the anti-matter plane, in a series of 1v1 matches. Quickly, demons and gods got favorite dungeons that they began cheering and betting on. Finally, whichever side managed to destroy the other plane first, would win a round. Then they'd just set up two more planes filled with new dungeons, before continuing. Each round would last hundreds of billions of years, but they were immortal creatures. Why would they care about time?
Bragging rights would go to the side that had more wins. Neither side was allowed to directly control the dungeons. Instead, at the beginning of every round, each side would be required to come together and negotiate a set of guidelines for the dungeons of both planes to follow. After a few rounds played out, both sides decided that wherever possible, both sides should cheat creatively, to make the games more interesting! The gods managed to sneak some celestial tree seeds down into the anti-matter plane, giving themselves more influence there. So, the demons set up some religious zealots in the same plane, fed them infernal mana, and controlled them to destroy both dungeons and celestial trees. Playfully incensed, the gods created the most powerful and mana-based apex predator they could possibly form in their matter plane, known as dragons, to hopefully destroy demons' dungeons. In retaliation, the demons found some creatures, pathalogically hell-bent on wholesale slaughter and destruction, in the anti-matter plane, known as devils, and started feeding them some infernal mana to strengthen and control them, destroying gods' dungeons. Eventually, both sides stole each other's new creature(s) to make guardians for their own dungeons. Quickly, devils and dragons could be found in both planes. At this point, feeling about even, both sides agreed to cool it a bit on the cheating, at least for this round.
Spoiler: History Spoiler Hints
But the gods secretly had one last play: a secret-ops black mission known only by the very, very few participating members. It was even hidden from the god king. After losing the previous two rounds, these gods were determined to ensure things went their way.