(3rd Person POV)
Just as the stars gave birth to their children, so the planets of the newborn Milky Way Galaxy eventually gave birth to lifeforms composed of matter, which began the long evolutionary climb to self-awareness, the first intelligent beings of the galaxy known to have developed a civilisation technologically advanced enough to cross the stars was a reptilian species of beings later called the "Old Ones" by the Aeldari, who knew them best of all their creations.
The Old Ones possessed a slow, cold-blooded, but still deep wisdom. They had long studied the stars and raised astronomy and physics to such a level that their science and technology appear now to Humanity like an arcane art. Their understanding of the universe's workings enabled them to manipulate alternate dimensions and undertake great works of psychic engineering.
Vael'Rothuun loved observing the Old Ones and their civilisation. He was there when the first one of their race evolved to the current state. He observed them and watched as they grew smarter and used their intelligence more and more. He was there when they first created the wheel and also when they advanced enough to not worry about dying of old age. Vael'Rothuun loved to simply watch and learn together with the Old Ones, whom he called the Toads. It wasn't their real name, but he liked to call them that.
As the Toads developed, Vael'Rothuun studied their success and managed to learn more about them and their technology. Technology was his bread and butter, thanks to the Essence of the C'tan, so he had no one in existence who could rival him there, but there was something about the Toads' use of their psychic energies that intrigued him. Vael'Rothuun was special amongst the C'tan. He did have a soul, in fact, but it was ... different from the mortal souls of the living beings who were starting to arrive. The Immaterium, which the Toads found, intrigued Vael'Rothuun, and he wanted to know more about it. To explore it and prepare, to have ideas for using and abusing it.
Therefore, he studied the Immaterium, where all the accumulated psychic energy came from. This dimension is more essential to life than anything else, as that is where souls come from and get their energy to survive. Without the Immaterium, nothing would be able to 'be alive'. The Toads developed increasingly, and their culture developed around scientific achievements—only the most innovative and most skilled held station among them. Time didn't matter for them anymore, making reproduction not very important to them. That would prove to be a mistake in the coming millennia.
The Old Ones were potent psykers who routinely used the powers of the Immaterium for a wide variety of technological applications. This included the construction of a system of instantaneous faster-than-light portals through Warpspace. These portals connected all of the Old Ones' colony worlds, allowing them to cross the vast gulfs of space with only a single step through the myriad Warp Gates they built to connect the worlds of the galaxy. This was a vast interdimensional network much like the Webway of today, which is its direct descendant, though on a much larger and more advanced scale.
Vael'Rothuun was there when it happened and when the Old One or Toad, called Rruprop, discovered it and presented the technology to the Masters. It was impressive to see such a young race, although they weren't as young anymore, developing such an intricate system to travel and achieve faster-than-light travel. All of the things he saw, Vael'Rothuun learned and tried to devise ways to use them for himself in the future. He knew that his brother, who is obsessed with fire, Nyadra'zath, would eventually come up with the Dolmen Gates to breach the Webway and achieve faster-than-light travel. But that wasn't what he wanted. He knew that the Necrons would rebel and turn against him and his brothers at one point. His plan was already ready, and he only had to wait and learn more.
The Dolmen Gates were unstable, and the Webway itself rejected them and the Necrons. The Immaterium seems to 'hate' the Necrons, for they have no souls. But that is where Vael'Rothuun comes in. He has a soul, and while he has a connection to the Immaterium, if he wishes, he doesn't naturally. This is good and bad for him. For one, he will never have to fear corruption as he is 'invisible' to the Immaterium. It is bad, though, since he will have to spend tremendous time and effort creating technology to utilise the Imperium for himself.
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Vael'Rothuun continued to watch the Toads like watching a series on Netflix. He moved around their colonies on different planets and watched the different characters in this 'show' to see who would develop something else. He was there when they first tried to create a new race entirely and when they sped up evolution for another. Their use in genetic engineering was ... acceptable in his opinion. Not good, but adequate. He had plans to create new races or elevate existing ones to do his bidding. He might also be able to give himself more than one body, so he would want the best he could get.
Through this network they created, the Old Ones spread their spawn to many places in the galaxy, but they also knew that all life was precious. Where they passed, they seeded new intelligent species and reshaped thousands of worlds to make them their own according to their predetermined environmental and geographic criteria.
The Old Ones' civilisation reached its height over 60 million standard years before the start of humanity's rise to glory and fall to shame. The Old Ones were responsible for the creation or genetic advancement of most of the galaxy's currently active intelligent species, and they also created the predecessors of the race that would eventually be known as humans.
Vael'Rothuun laughed when he saw it happen. He witnessed the origin of humanity, and he saw the primitive ape-like creatures created by the Toads. It was a fun time for him, but he was aware that they had reached their peak when a fateful encounter told him that it was time for his plan to start soon.
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The humanoid species that would become the Necrons began their existence under a fearsome, scourging star in the far reaches of the galaxy known as the Halo Stars region, billions of standard years before Humanity evolved on Old Earth. Assailed at every moment by solar winds and intense radiation storms, the flesh and blood species known as the Necrontyr became a morbid people whose precarious life spans were riven by constant loss. Their lives were short and uncertain, their bodies blighted and consumed at an early age by terrible cancers and other illnesses linked to the high levels of ionising radiation given off by their sun.
Necrontyr cities were built in anticipation of their inhabitants' early demise, as the living were only brief residents scratching out a living in the shadow of their ancestors' vast sepulchres and tombs. Likewise, their ruling dynasties were founded on the anticipation of early death, and the living were thought of as no more than temporary residents hurrying through the more permanent and lasting structures raised to honour the dead. On the Necrontyr homeworld, the greatest monuments were always built for the dead, never the living.
Driven by necessity, the Necrontyr escaped their crucible prison and struck out for the stars, hopeful of carving out an empire in which they could realise their species' freedom from the lethal energies of their birth star. Using stasis crypts and slow-moving, antimatter-powered torch-ships that were clad in the living metal known as Necrodermis to resist the millennia-long journeys through the void, the Necrontyr began to colonise distant worlds.
Little by little, the Necrontyr dynasties spread further until much of the ancient galaxy obeyed their rule. From the earliest days, the rulers of individual Necrontyr dynasties were themselves governed by the Triarch, a council composed of three Necron dynasty monarchs known as Phaerons. The head of the Triarch was known as the Silent King, for he addressed his subjects only through the other two phaerons who ruled alongside him.
Nominally a hereditary position, the uncertain life spans of the Necrontyr ensured that the title of Silent King nonetheless passed from one royal dynasty to another many times. The final days of the Necrontyr Empire occurred in the reign of Szarekh, the last of the Silent Kings.
Sometime during their slow interstellar expansion, the Necrontyr encountered an ancient species far older than any other in the known galaxy. These beings were the Old Ones - absolute masters of forms of energy the Necrontyr could not even conceive of, let alone wield. The Old Ones had long ago conquered the secrets of immortality, something greatly desired by the Necrontyr, who yet bore the genetic curse of the bitter star they had been born under.
.
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(Vael'Rothuun POV)
On a distant planet, the Toad Bruupro spread new life and improved the fauna when another spaceship appeared in the distance. Judging by its speed, the look of the craft, and the species on board, I can tell that this one is not from the Toads. Using my insane senses, I can 'see' who is now approaching the planet.
Haha, it seems it is finally time for me to start my plans soon. The Necrontyr have arrived, and their first encounter with the Old Ones is about to occur. How lucky I am to witness it. The show was getting rather dull in the last century, and I am glad they are introducing new characters.
I observe the Necrontyr ship landing on the planet, and a small group approaches the Toads. It's amazing that they can still walk with the amount of radiation they emit. No wonder they have such problems. Their entire genome has been altered to this degree, and they don't get rid of it properly. The best way to do that would be to either use advanced genetic engineering and change it drastically or separate the ones who suffer the most from the rest and let them die out.
However, that wouldn't work well since their DNA is broken in far too many places, and evolution is basically impossible at this point. Poor bastards. If only the Toads were as friendly as they proclaim to be. The entourage bows before Bruupro and shows their respect. One of them starts to talk in a hoarse and throaty way, speaking of the pain any form of movement causes.
"Oh, great beings. We, the Necrontyr, greet you and are honoured to stand in your presence. We come before you as a beaten species. For millennia, we have suffered at the hands of our planet's cruel star and its radiation. It has made us weak and short-lived. Oh, great ones. We have witnessed your immense power and the skill with which you subdue different energies to your will. It is our hope that you-"
"Hmm, indeed, you emit a lot of radiation, bruup. Please don't come any closer, bruup," the Toad says and turns away from the Necrontyr.
Haha, look at that. For a long time, the Toads were successful and the dominant species in the galaxy, to the point that they had forgotten how to address those less fortunate. Greed is a galactic and universal constant. It will affect most species that haven't achieved the perfect balance. And since such a thing doesn't exist, it will always exist. From it, conflict will come, and it is now closer than anyone realises.
"We are aware of our condition, oh great one, and apologise for this. But please, you are wise and brilliant beyond our imagination. Is there a way for you to share with us the secrets to your immortal existence? All we desire is to be free of pa-"
"You are addressing, Grand Discoverer IIIrd degree of Health and Earth sciences, of the Baobbob Infinite Trancendency, bruup. Don't address me the way you do, bruup. We have discovered all of our technological science ourselves, bruup. And there is no chance we would give it to you for free, bruup. Do you understand, bruup?" the Toad answers.
"Bu-but great one, we-"
"Silence, bruup. I care nothing for your pain and suffering, bruup. If anything, it is embarrassing for you to still exist in the way you do, bruup. You should simply accept that you have lost the evolutionary fight, bruup. And die, bruup."
The Necrontyr look surprised and embarrassed. They were prepared to give anything for this knowledge, and yet here they are, being sent off so brusquely. I can't judge anyone here, since I don't care, but I would describe this as sad not only for the Necrontyr, but also for the Toads... and the entire galaxy. Because what follows will give rise to disgusting and chaotic consequences.