There is a story, told from one end of Remnant to the other, of how the God of Light forged the world from nothingness. Founding it upon four ideals: creation, destruction, choice, and knowledge.
However, his work was not yet done, for a world needed inhabitants. So he created all manners of animals and scattered them throughout the world to live and grow. Yet this was merely the beginning of the God's plan.
Next, the God of Light reached out to his younger sibling, entreating him to help create beings who were neither Light nor Dark, but both. A perfect hybrid encompassing the four ideals the world revolved around.
While initially skeptical, the God of Darkness quickly came around, curious as to what such beings might become. Together, the Brothers gathered up countless motes of their essence and shaped it into a bipedal form.
The God of Light breathed the spark of existence into the being, while the younger of the pair imbued their creation with a fraction of his chaotic essence. The combination of the two forces granted the creature nigh-immeasurable potential and the ability to channel the energies of their soul to perform wondrous and terrible feats.
And so, the first human was born. An unprecedented and outright contradictory existence, the first species born of cooperation between the brothers rather than competition.
Satisfied with their work, the pair cast their power out into the world, forming hundreds if not thousands of such beings. Each one unique, for even if they shared a gender, bloodline, or mindset, no soul could ever truly be the same.
And so, humanity grew and thrived as time went on. Overcoming whatever challenge they faced, be it the environment, the Grimm, or even their fellow man. A story of triumph, failure, and determination that continues to this very day.
But it isn't the only one of its kind.
After all, humanity might have been the Brother gods' greatest work, but that doesn't mean they were the first species they created. Or even the last.
No, the title of 'eldest' belongs to the Lunarians, though that name came later. For you see, the God of Light didn't immediately go off and request his brother's aid. No, he made his first attempt at creating a new species long before humanity was an idea.
Despite looking like particularly attractive humans, they were far removed from their younger cousins in nature. Blessed with agelessness, divine power, and exceptional bodies unhindered by disease or frailty, they were a race who surpassed all others.
In mere decades, they forged an empire that spanned their entire continent. Within a meager two hundred years, they were the uncontested rulers of the world. Possessing an understanding of science and mysticism so great that even their creator acknowledged their potential to one day grow beyond him.
However, despite their countless blessings, they suffered one debilitating flaw: their purity. As beings born solely from the power of a being embodying creation uninhibited by destruction, they weren't particularly inclined towards change or degradation, viewing such occurrences as 'impure.'
Oh, they could still pursue knowledge and understanding to their heart's content, they wouldn't have become as advanced as they did if they lashed out against every discovery, but things that would change themselves were not looked upon fondly.
After all, were they not pure beings? Was it not true that impurity could only lessen them?
It was, admittedly, not a claim without basis.
Their civilization had developed to the point where wants were non-existent and everyone lived a life of peace and enjoyment. Why risk jeopardizing that?
And then there was the physical aspect of that aversion...
Despite the Lunarians' inherited essence, which ensured that they would not grow beyond their prime and only unnatural causes would end their lives, some of them had begun to show the earliest signs of the slow death afflicting every other being.
The purity of the God of Light's children was certainly potent, but it was not so great that it could not be affected by outside forces.
Living in a world where all life but them would decay in time, where death pervaded everything beyond the walls of their territory, meant that the spiritual landscape slowly wore away at their immutability. Weaving death through their beings until it's as much a part of them as it is everything else.
As you might imagine, they were far from happy with this discovery. In an effort to escape this fate, their greatest scientist led a project to determine everything that could spread the impurity they battled against.
The results were less than promising. Not only was death and decay a nigh-omnipresent source of impurity, but illness and actions which violate spiritual tenets could also spread the infection.
Faced with the reality that the world was inundated with death and that exposure would slowly kill them, a sage named Tsukiyomi devised a plan. As impurity was an unavoidable part of life, he and his people would leave behind the world and colonize the moon. Which lacked the touch of life, and thus impurity.
To this end, he went to his teacher, the aforementioned scientist, and enlisted her aid in his endeavor. With her knowledge and reputation combined with his charisma and status, they rallied the populace to their banner and turned what seemed like a far-off dream into a reality.
Within months of Tsukuyomi's fateful decision, they had not only reached the moon but built a new home upon it: the Lunar Capital. In honor of his work, he was declared their unconditional leader, his people forever grateful to him for saving them from their fate.
In honor of their new home, they renamed themselves the Lunarians, eschewing whatever title their creator had given them in the process.
With their exodus complete, only one task remained before they could truly settle into the new lives they had so desired. Removing what had been left behind in their flight.
Whether out of antipathy towards the world they had left behind, the simple desire to ensure that what was theirs would remain unsullied by the world's residents, or something else entirely, the remains of their pre-Lunarian days needed to disappear.
And disappear they did, wiped away in a rain of cleansing light from the heavens. Leaving behind nothing but barren land where there had once been thriving cities and advanced knowledge.
As you can imagine, the God of Light was less-than-pleased. While their achievements were undeniable, the fact the Lunarians alienated themselves from any other life but their own or their creations was beyond disappointing.
So great was his disdain for the Lunarian's chosen path that the elder Brother traveled to the Lunar Capital and spoke directly to their leaders in the hopes of convincing them not to shut out the rest of existence. Yet, his efforts would be in vain.
The Lunarians respected and revered their creator, but refused to change their minds. Stating that, while the God of Light may be great enough to remain unspoiled even when touched by impurity, the Lunarians themselves were not so fortunate.
In their minds, he was simply too far beyond their concerns to understand why they were so adamant on the matter. And as such, the God departed the Lunar Capital with a weary heart, knowing that he would not be able to convince his creations otherwise and unable to bring himself to force them.
He had created a race of perfect beings, but that very perfection prevented them from fulfilling the role he had created them for. The Lunarians would build countless wonders and understand innumerable truths, but they would never grow beyond the bubble they had made for themselves.
It was a tragic irony that the most advanced race the God of Light had ever witnessed would rather isolate themselves and simply exist rather than experience life. Out of respect for their achievements and affection for his creations, he opted to leave them in peace and not interfere with them in the future.
Having witnessed the pitfalls of perfection, the elder Brother realized that his approach with the Lunarians had been flawed. He could not simply grant his creations everything they could require, they would need to work for it. To be able to touch the impurities of the world without recoiling or being consumed.
And so, the God of Light went off to request the aid of his younger brother in a joint project. Confident that a being created from both of their aspects would be able to succeed where the Lunarians fell short.
You already know how that worked out, with the creation of humanity and the new race spreading out across the world. Establishing their own civilizations, cultures, techniques, and growing into a thousand new possibilities every day.
As the Brothers watched over the newborn humanity, the elder of two privately hoped that they might one day reach out to the Lunarians and come together as one. That the innate mutability of humans could allow them to bridge the gap between the two races.
Yet, despite those dreams, the Lunarians never left the moon, content to gaze down on humanity in disdain and disgust. Though they never did take action against their sibling race, for they deemed purifying the world to be far more effort than it was worth.
A handful of Lunarians did eventually leave for the world below, though that's best covered another time, but in the end, the first creations of the elder Brother would never break their isolation as he had hoped. Truly, a waste.