For almost four thousand years after the Second Cleax Invasion, the Cleax were quiet, until suddenly, without warning, they swarmed once again in A.E. 574. This time their massive fleet headed spinwards, tearing through the United Atarsid Nation before getting stopped at Starforge by the surviving Rek and the full might of the Serene Empire of the Ait Benir, with assistance from the Ibyssian Brotherhood, Zinari Imperium, and, surprisingly, the Iron Corsairs.
The alliance pushed the Cleax back until they were occupying only the very southwestern (rimwards + antispinwards) part of the sector. Victory seemed imminent.
The Sarkeen
It was then that Starmourn was first introduced to the Sarkeen - the second form of the Cleax, heretofore unseen.
We do not know what the Sarkeen are. We don't know if they rule the Cleax, as some have speculated. We don't know if they are even the same race as the Cleax, though it is believed they are, and they are typically referred to as such. Do the Sarkeen begin as a normal Cleax, and evolve? Were the Sarkeen intentionally mutated by the Cleax? Are they nothing but extreme genetic outliers among their race? We don't know.
What we do know, and what was discovered during this Third Invasion, is that they are the greatest weapon the Cleax possess. Though apparently few in number, the Sarkeen are enormously powerful, each acting as effectively huge, living starships with a crew of one.
A Sarkeen looks like an absolutely massive, mutated normal Cleax, with a gaping maw, multiple long tentacles that look like mutations of the many ‘arms’ of a normal Cleax, and long tentacles. Although we've never captured one, they appear to move via some kind of internal plasma railgun system. They generate plasma, somehow, and then shoot it out of orifices on their body at incredibly high speed, though using what mechanism, we don't know, propelling them forward. They're similarly able to deal immense damage by firing near-steady streams of plasma at opposing starships through their multiple tentacles, each of which is centrally controlled by the Sarkeen's single brain, and which act together with perfect coordination.
The Sarkeen protect themselves in a variety of ways - they can generate powerful bio-electric fields that act as shields and that is widely believed to be a product of their own flavor of star kith, they can release swarms of incredibly destructive clouds of 'spores' that attach themselves to any metal object and quickly begin reducing it to component atoms, and they're able to generate singularly powerful EMP (electro-magnetic pulse) bursts to disable nearby ships or drones.
As the alliance opposing this Cleax invasion fought to secure what appeared to be imminent victory, a handful of what we now know are Sarkeen arrived at the battle site, to the galactic southwest of the M'hamid Cluster, at the Voidgate we simply know as the Cleax Gate today.
At first, the opposing forces weren't even sure the Sarkeen were a weapon. Perhaps these were their leaders, come to negotiate an end to the war, they wondered, though all previous attempts at communication with the Cleax had been ignored - they weren't even sure if the Cleax were receiving their signals. Warily, they allowed the Sarkeen to approach the flagship of Emperor Lin Sber'ana of the Ait Benir and his complement of guardian starships.
The Battle of the Sarkeen
Suddenly and without warning, the Sarkeen unleashed their biological EMPs, powerful enough to overcome the defenses of even the mighty Phoenix Cruisers that make up the core of the Ait Benir's fleets. Almost simultaneously, they poured their spore clouds into space around the ships.
The rest of the alliance immediately moved to begin attacking the Sarkeen, but to the horror of all, it was too late for the Emperor's flagship and the core of the Ait Benir forces. Within minutes, the starships exposed to the stores began to disintegrate from the outside in as the armor shielding around the superstructure was quickly eaten away at. Great gouts of escaping atmosphere pointed to each fresh wound a ship, and quickly thereafter it wasn't just atmosphere, but bodies as well.
The Sarkeen also began immediately opening fire on any enemy ship in reach, targeting and destroying dozens in the first salvo, after which they were quickly supported by the rest of the Cleax forces. The sudden reversal of fortune threw the opposition forces into disarray, and as they re-organized their command structure, now under the leadership of the famed Corran Admiral Ilmus Argo, leading the Ibyssian Brotherhood forces.
They threw their might at the Sarkeen and the other Cleax, but found themselves overwhelmed. In desperation, Admiral Argo ordered all forces to concentrate their firepower on the Sarkeen, and to ignore the other Cleax forces. It was a strategy sure to cost them dearly, as the Cleax forces would be free to simply flank and open fire, but as it was the Sarkeen who had tipped the scales from imminent victory to imminent defeat, he felt the risk had to be taken.
In the end, it was the Rek and the Lha Ti that saved them. The Rek, one of the Elder Races, though few in number and much-diminished as a civilization since they were nearly wiped out by the Ishvana during the War of Extinction, are immensely powerful masters of star kith. Meanwhile, the Lha Ti - the eldest of the Younger Races - were created by the Utan Mir to produce the most powerful concentration of void kith they could in a single entity.
The few Lha Ti present at the Battle of the Sarkeen were among the most powerful of their race, able to survive deep space and propel themselves with void kith alone. They made directly for the Sarkeen, one of the few other races capable of surviving in hard vacuum minimal equipment, and certainly the largest they had encountered. The Lha Ti themselves are enormous creatures who spend most of their time underwater where their bulk is supported, and while the Sarkeen are yet substantially larger, the Lha Ti are simply unequalled in their mastery of void kith. Just as importantly, they are biological beings, and are unaffected by the EMPs and the spore clouds the Sarkeen possess.
The Lha Ti began to unleash raw void kith on the Sarkeen, trying to crush the life out of them, who retaliated with blasts of plasma, gravely burning many of the Lha Ti. Bravely, for they were in ships vulnerable to the Sarkeen, the Rek moved forward, adding the heat of the stars to the attack on the Sarkeen, shattering their bio-electric shields.
On seeing their shields go down, Admiral Argo ordered the rest of the fleet, which was taking a pounding from the Cleax flanking them, to move in. Long-range railguns from the Zinari, swarms of baryon missiles from the Iron Corsairs, void bombs from the Corran and the Ixodon of the Brotherhood, and the Ait Benir's phase cannons soon competed with the spears of starfire hurled by the Rek and the crushing force of the Lha Ti.
Three Sarkeen fell under this onslaught, and suddenly, entirely without precedent, they began to pull back, taking the rest of the Cleax with them. Admiral Argo ordered his forces to continue pouring fire into the retreating Sarkeen and Cleax, but not to pursue. Between losing Emperor Lin Sber'ana and the immense losses taken by the forces opposing the Cleax generally, Admiral Argo saw little gain in risking pursuit. This could be a genuine retreat, or it could simply be a trap.
The Aftermath
As was soon discovered, it wasn't a trap, but the Cleax also had not retreated very far. They appeared to be settling in, taking up residence in multiple systems in galactic southwestern Starmourn. The races of Starmourn, both those that had participate in this third fight against the Cleax, and most of those who didn't, discussed what to do. The Cleax presented a danger to everyone such as hadn't been seen since the Ishvana nearly wiped out the Elder Races ~37,000 years prior.
It was decided, reluctantly, that the Cleax would have to be permitted to remain, even though they now controlled a Voidgate, potentially giving them access to those other Voidgates not protected by Aegispheres, on Starmourn's fringes. Although there were many voices who loudly counseled eradication, such as the Iron Corsairs and the Selassian Dynasty, and what was left of the United Atarsid Nation, calmer voices prevailed. It was felt by most that the problem with attempting to wipe the Cleax out was a challenge of unknown scope. None knew where the Cleax originated from, how many more there were lurking out there, and what their overall capabilities were.
The decision was made to leave the Cleax to themselves, but to carefully watch the Voidgates adjacent to the now-named Cleax Gate for any signs of aggression, and for the several hundred years since then, there has been none. On the other hand, the Cleax are now present in galactic southwestern Starmourn in numbers far greater than during any of the invasions, and their potential is an issue of permanent concern among the races of Starmourn.