Alin Breeding Reservoir

The Alin were a race that had a symbiotic relationship with mould that grew beneath the surface of their skin providing nutrients. Born externally via soft skin eggs in breeding reservoirs, over the the millennia the fertility rates of the Alin declined, until by the end of their star-spanning empire only their 12 "homeworlds" and Holocene contained breeding reservoirs that could still produce viable progeny for the Alin.
Over the 4,500 years that the Alin have been locked off from the remainder of existence, all the reservoirs on their homeworld have ceased producing young. Only the world of Holocene contains breeding reservoirs that remain viable. And they were built during the reign of the Carkade Empire and remain hidden to the current occupants of Holocene. The exact nature of the mould and why it now only exists on Holocene is also unknown.
What is known is that the Alin are dying. They are xenophobic, regard all others as "things", even those they're allied to, and that they must endure only as long is necessary unless they occupy Holocene and subsume it completely during the current Discontinuance Event or they will cease to exist.
They were always fractious and in constant conflict with not only others of their kind, but all others, but now faced with a final existential event, those that still remain on the original 12 homeworlds are dedicated to the occupation of Holocene and the hidden breeding reservoirs that are their future.

Alin Breeding Matron fusses over the Alin embryos in an Alin breeding reservoir