I have written in other places in the Citadel about the fact that the Cosmic Era is creeping towards a technological extinction level event, ala garnering the attention of something that humanity cannot survive, like an actual outer god. I have also written that parapsychic ability and arcanotech draw their functionality from the River of Sorrows, an aspect of reality that itself is powered by the suffering of sentient beings.
The parapsychic is an entity in transition, not entirely unlike the larvae of the outer gods, their abilities manifest, and they become more powerful, they employ arcanotech to enhance and accelerate their modification, because the ultimate goal, the basal urge, is for a metamorphosis. The most powerful parapsychics, the proposed arhats, the mortal demigods, will move beyond black and white morality, traditional mortality, and will eventually shed their humanity, they will become creatures of the River of Sorrows.
The attrition rate for this transformation is appalling. The success rate is astonishingly low. Most never gain the power and potential to reach the critical threshold for this level of transformation. Of those who do, some turn away, choosing their native race over transcendence, or they choose to transcend and must survive their own race attempting to destroy them. This can be a fear reaction, non-transcended parapsis knowing what they are doing and fighting them, or their actions drawing the attention of something else beyond their world/plane of existence.
The former mortal undergoes their metamorphosis and the thing that comes out on the other side is a a small outer god, a Seraphim as per the submission.
Over time, a seraphim gains strength and power, it faces the rest of the cosmos and finds its place.
This isn't flying away into the ether so much as it is becoming a megapredator and dominating their area of emergence, usually starting with their homeworld. The can be an extinction level event, with all but the most basic forms of life being wiped out, it can be apocalyptic with the seraph making itself the leader of the world, and brutally subjugating it. In some shark species, the unborn shark pups will gestate and eventually start feeding each other, until only the strongest pup survives and is carried to term, and thus most seraphs are destructive of their home environs.
Erelim are transcended teratomorphs
Some of the most epic comic big bads are basically seraph of varying degrees of strength, ala Darkseid, Thanos, Doomsday, Apocalypse, etc. A good sign is being 50% bigger than other characters, being immortal or being beyond the normal ability to be killed, fantastic ability to come back from seeming death.
The Escape Pod: A civilization has a nascent seraph, they can't kill it, and they know containment is only temporary. Rather than increasingly complicated traps and tombs, it makes sense to load the dormant seraph into a container and send it as far away from the homeworld as possible. The tomb ship is made as secure as possible and is sent into one of three places
SHOOT IT INTO THE SUN! - and hope the fury of the stellar environment destroys it like your civ couldnt.
Shoot it into a gas giant - and hope that even if it is not crushed, it can't escape the gravity and dense atmosphere
Shoot into deep space - and let it be someone elses problem in 10,000 years
This is where things like the hashmallin come from, their bodies ravaged by nuclear fury until they gather enough strength to emerge, but as mindless destroyed things with only fury, hunger, and pain as their sole drives.
This is also how space dumpsters show up and disgorge cosmic horrors. Not everything fired off into space actually was a seraph, some were close, some just turn into monsters, etc.
Then there is the issue of just what are the Elder Gods, in the Lovecraft mythos, when they are blended into the Cosmic Era universe, and the answer is simple as it is terrifying.
The Universe is cyclical, and it dies and is reborn on a regular schedule, but on an order of tens of billions of years, and there are few things capable of altering this pattern. In each incarnation of the universe, the outer gods arise, sentience arises, and the universe moves on, until it begins to decay, and there is the death of the universe. Like the phoenix, it is reborn from a new big bang. very few things survive the death of the old universe to transition into the new one.
When an outer god is able to pass through the membrane between the universes it becomes an elder god, as it carries everything it had into a new universe. Being immensely powerful in a universe that is still sorting itself out, the Elder Gods are the ones who get to make the momentous incidental decisions that will echo through that incarnation of the universe.