Back when Paradise existed, Promathia absorbed the Emptiness, subsequently causing his own death. Altana, in an act of love, used the power of the true crystal on Promathia's corpse, banishing his Emptiness and creating the Ancients.
Fast forward to CoP, Selh'teus revealed that Yve'noile planned on absorbing the Emptiness from the Chamber of Eventide. Nag'molada, believing her eternal slumber was a result of this, rebuked with: "And you let her commit this act!? Lady Yve'noile is not to blame! She built the Chamber of Eventide in the name of love! She tried to rescue us from our fate!"
The operative word being love. In an act of love, Yve'noile also banished the Emptiness from within the Kuluu through the creation of the chamber. Furthermore, Mildaurion revealed in the mission Dawn that Yve'noile had even witnessed Altana's true form: "The Dawn Maiden Yve'noile has memories of witnessing the true form of the great goddess Altana."
However, Selh'teus immediately corrected Nag'molada, and mentioned how he intervened by becoming the sacrifice instead: "You speak the truth. We Kuluu are at the beginning of all of this. That is why I absorbed the Emptiness from the chamber... I sealed it within me, and departed this life."
By absorbing and sealing the chamber's Emptiness within himself, Selh'teus also subsequently caused his own death. And just like Promathia, he also sought his own resurrection. Nag'molada immediately followed up with: "You...died? But...you're still...?" Which is then answered by Prishe: "Phoenix... Phoenix was with you, right? She brought you back to life."
Taken altogether, this demonstrates some really interesting parallels. But more than that, if we infer from Selh'teus' actions that Promathia also made a necessary sacrifice to stop a greater threat when he absorbed the Emptiness, then that introduces an ironic twist.
For instance, if we assume the theory that Promathia sacrificed himself to stop the Cloud of Darkness is true, then that means Promathia became the very thing he sought to destroy by perpetuating a cycle where Selh'teus was forced to make the same choice to stop him.
And on a more thematic scale, this goes along with how the same tragedies appear to unfold time and time again: the creation of the Ancients led to the Zilart/Kuluu schism, which led to the Meltdown, which led to the creation of the five individual races, which led to a schism between those five races, which led to the Crystal War, which led to several more tragedies unfolding, and so on.
