The Numen Cataclysm was both a world-ending and creation event long before history, estimated to have occurred some several million years ago. This story has been passed along through generations and adapted based on several centuries of cultural analysis on the part of the Consortium of Ancestral Preservation (CAP). The Numina crafted a weapon of mass destruction, the Malumastra, and used it against their Progenitor adversaries, shattering what was once a single material plane into billions of smaller celestial bodies that would eventually become the stars and planets of the Caelum Galaxy. In order to save the universe from continued destruction from the Numina, progenitors cast an eldritch curse on them and sealed them away all across what was left of the Prime Material Plane, in the hopes that the children of the Numina would never gain the power of their forebears and use it against the galaxy again.
Before the Cataclysm
Prior to what we know as the Caelum Galaxy, there was only the creatures we know as progenitors and the Prime Material Plane. Several cultures refer to the progenitors as the 'olden gods' of our existence, and the title is easily supported by stories of life prior to the Numen Cataclysm. These stewards of the Prime Material Plane were ubiquitously known to create and nurture its inhabitants, creating what the CAP understands as a paradise of order and benevolence. Rather than have several planets, it is understood that the Prime Material Plane was once a coherent plane without any space, or Aether, in between.
The progenitors were alone up until one point where the Numina were brought into the equation. It is not understood how the Numina came to be, but the likely theory is that the Numina are offspring of progenitors to some extent. Many stories allude to the progenitors being scholars and attempting to understand the magic of the universe, so it wouldn't be surprising if the Numina were a byproduct of experimentation on their own species.
Conflict
In almost every story known, the Numina represent the aspects of sentience: greed, malice, benevolence, apathy, peace, and the like. Some Numina embody these aspects passively in their legends, while others are staunch bastions of that trait. The latter was true for an Asbris, the supposed Numen of Death. The Numina, as the progenitors, did not die by age, and fighting between the Numina and their forebearers was nigh unheard of. It seems the Numina were brought into existence at different points, due to the fact conflict had not occurred until Asbris, Ihmir the Numen of War, and Enoch the Numen of Zealotry declared war on the progenitors.
From the declaration of war, it is believed that the Numina were split in who they wanted to support. This created an imbalance, a gap in power Asbris wanted to close. The war between progenitors (and their supporters) and the rebelling subset of Numina leaned towards the progenitors quelling those fires fairly quickly, unless Asbris and his followers found some way to even the playing field. As a result, a series of Astra, weapons of insurmountable power, were created. Despite these creations leveraging massive amounts of power, war continued to ravage the Prime Material Plane with no end in sight. This was when Asbris dedicated himself to creating the Malumastra, a spear capable of causing enough destruction to tear an entire plane of existence asunder.
It is unclear whether the Malumastra was wielded immediately after it was forged, or whether peace talks with the progenitors ever occurred and subsequently failed. The stories compiled only agree on a blindingly strong blast of radiant energy engulfing the Prime Material Plane. What remained were scraps and pieces of a once beautiful plane, that of which have become the planets and stars in the Caelum Galaxy. The progenitors reacted by sealing the Numina away in the ruins they created. Additionally, a curse was placed on them, such that their offspring could never attain the full power of a Numina and create more Astra in retaliation. As a result, the creatures that spawned from the Numina could only embody one half of their ancestors unrelenting power, bringing about the first celestials and erinyes that would then produce Aasimar and tieflings. From the ashes of a single plane, the progenitors worked to make do with what they had left, supposedly creating the ecosystems of flora and fauna we see across the galaxy today.
Aftermath
Millions of years have passed since this event was claimed to have occurred. Progenitors (or presumably their descendants) are still found in various capacities about the systems, with the vast majority of encounters occurring out in the Terminus. As for the other side of this conflict however, no sighting of the Numina has been confirmed by the CAP. Astra, including the Malumastra, have also yet to be found. The children of these fallen immortals, the celestials, erinyes, aasimar, and tieflings, can still be found scattered across space, living their lives as they believe the Numina would have intended. This creation story has become increasingly more relevant to the CAP and its Intergalactic Federation (IGF) superiors as a result of the Seraphic Inquisition, a relatively recent movement of celestials vying for control of the galaxy under one zealous banner. It is the IGF's hope that through continued support of CAP initiatives, we can better understand the history of the celestials, the Numina, and the progenitors in order to stop them from enslaving sentient life as we know it.