The most common question I am asked as an officer of an Atlantean starship is why I left Earth. They are really asking why I gave up the guaranteed prosperity and safety of the home system, trading that for uncertainty on a starship, skulking through the ruins of dead civilizations, exploring dead world after dead world, haunting the void between the stars like a forlorn dandelion seed, blowing through a concrete lot measured in petameters (1 petameter = 0.105 light years, 1 light year = 9.5 petameters). The answer is simple and complex, sadly. As a younger man I was driven away from the magnificent cities of the inner system, I was born on Earth, and largely grew up in one of the hives, in the Europolis
The Human Hiveworld
The distant future of Earth is to become studded with eperopolises, or continental cities. North America develops three eperopolises, consisting on the Eastern seaboard, Western seaboard, and the southern Mexican supercity that extends down into the isthmus of Panama. The same goes for Asia, Europe, and Africa. By this point more than half of terrestrial humanity lives in seacologies and geofronts. Only the still persistent ecologism of the now defunct Cosmic Era retards the development of a proper Ecumenopolis on Earth. There is still a great deal of value placed on greenspace and bluespace. The rest of the Solar system is heavily populated, with terraformed Venus and Mars have large populations. Another large segment of the human population lives in permanent artificial habitats orbiting various planets or even directly orbiting the sun, some of which measure in dozens of kilometers in size. There are numerous megastructures across the solar system, including space elevators, and smaller planetary bodies like the Moon, Mars, the Jovian satellites, etc, sport Niven rings around them.
The Megaroad Project
Approximately 800 years ago, humanity, when it was still a binary species, started building generational starships and launching them into the void. These ships were at the time, massive, some were nearly a kilometer long. While not impressive compared to the things in the Solar System today, at the time of their launch, they were the largest self propelled constructs humanity had managed. These ships carried large food stocks, a population that would reproduce over the duration of the voyage, so that the sixth to tenth generation of crew would see the ship reach it's destination. It was a valiant but doomed effort. Our retracing of the navigational records and discovering the navigation and communication relays they left behind them allowed us to find almost all of the Megaroad ships launched. Of the 16 ships launched, 9 'died' in space. Several succumbed to mechanical failure, an asteroid strike, outbreaks of disease, and most commonly, mutiny among the crew. Of the seven ships that reached their destinations (impressive considering the primitive technology) five found worlds that were completely unable to support life. You don't lonely until you walk through the ruins of a colony that failed, 16 light years from Earth, and you find the skeleton of the last colonist. Poor fucking bastard. Of the four worlds that were suitable, two failed for social or resource issues, and the last two were eaten.
Not cannibalism, but they were discovered by something out there in space, and it came down on them, and devoured them.
The Ishim aren't a species of exomorph, but rather a conglomeration of similar phenomena that scientists haven't decided are lifeforms or not. Something keeps the Ishim out of the Solar System, so they were not encountered until we reached beyond and into the gravity wells of other stars. They are ribbons and filaments of light, sometimes a hundred thousand kilometers long. They are aphasic in nature, but unlike star whales they show no exobiology, no feeding or mating, and do not respond to stimuli. They do produce a strange radiation that attracts space spores, and staying too close to one for too long does tax the shielding of even the most powerful ships.
Thus far, we have encountered a single seraphim classed entity. It was formerly one of the colonists at a now classified planet. It had been surviving without food or supplies for close to a century by the time the survey ship found it. No longer human, it was filled with an alien hostility and energy, demonstrating long banned parapsychic powers and manifesting abomination level abilities. The survey team was slaughtered and their ship was taken. The entity attempted to board the survey ship, but rather than allow something as apocalyptic as the seraph aboard, the crew opted to self-destruct the vessel. The status of the seraph is not known, no probes sent to that world have sent back any information regarding it.
The Cosmic Era, dabbling in things they shouldn't have, almost starting making seraphs, on purpose. They had no idea the destructive capability of those entities, fusing divine energy with mortal flesh. They had no idea the extent and truth of divinity, and sought to harness it's power to further their own. It is no small wonder that they didn't snuff out the human race before being turned back, and their blighted technology buried.
One of the toxic side effects of the Cosmic Era's addiction to arcanotech was the regular manifestation of teratomorphs, or kaiju. Massive, powerful, destructive, these entities caused vast amounts of damage before being destroyed. The erelim are what happens when something like a terrestrial teratomorph has enough time to advance through it's life cycle. They are somewhat larger, but their abilities and much more manifest, and their divinity is greater. Erelims have cleaner lines, and demonstrate parapsychic ability sufficient to destroy cities with ease. Had an erelim manifested during the Cosmic Era, humanity wouldn't have had a way to fight back against it. Unlike teratomorphs, erelim are nigh indestructible. While their bodies are tough and durable, they have a 'Dirac Solenoid' at their core. This construct is the element of divinity, giving them access to limitless power while being almost completely invulnerable to terrestrial weaponry. Comparatively, teratomorphs lack this organ, and must feed to replenish their power, and can be worn down and driven back.
Finding erelim isn't terribly difficult. Eliminating them is a bit more complicated. There are two potential methods for dispatching these little gods, sending a tamed god to kill it, or to take one of the relic weapons down to where the erelim is and dispatch it personally, usually in a warstrider. It's tricky, usually several warstriders armed with Gram blades attack after the erelim has been bombarded from a distance. The best tactic involved high yield blast weapons followed by a volley of high energy beam weapons while the warstriders close in. Still usually lose half of the mecha involved, even when it goes to plan.
Most of the Angels from Neon Genesis Evangelion would qualify as Erelim, but Sachiel, Matariel, Gaghiel, and Zeruel are prime examples of Erelim. In context, teratomorphs are drawn from the Toho Godzilla universe. While powerful, they are no match for the erelim.
The Hashmallim are powerful beyond imagination. They are also disturbingly common. To find Hashmallim, you just have to go looking near a star, you'll find them there. They are massive, the smallest are hundreds of meters of long, while the largest are dozens of kilometers in length. They feed on solar radiation, and when something interesting comes into their field of perception, they will more towards it and attempt to devour it. Another disturbing fact about them is that the longer a particular entity faces something, the more is assumes it's shape. After a prolonged engagement, a hashmallim chasing a starship will have features resembling the starships. Likewise, they will manifest attributes of the things they consume. In their natural resting form, they are fleshy spheres, with random spikes, cilia, and other primitive structures. The colonies that flourished for a short time were both found the hashmallim, and the divine descended on those planets and devoured the colonists and wrecked most everything on the ground.
The Hashmallim, bastards. You can sit on the edge of the system at Kepler 12, and you can look at them. You can see the ones that did it. One of them has a human face, 1300 meters wide, but still a human face. It moves, the boffins read it's lips, and are writing down the words it is mouthing in space. They think it might be trying to communicate, but I think it's an abomination and needs to be pushed into Kepler so that it burns up, until even it's core explodes from the heat. There are others, one with human arms, another has legs sticking out of it. Six hashmallin, six with human traits. Burn them all.
The Hashmallim have a final trait that makes them a living nightmare, they spawn. These spawn are not more Hashmallim, thankfully. Instead they create magnaspawn, smaller and more specific versions of themselves. These lesser hashmallim are tough but not unstoppable, they are organic and divine, but lack dirac solenoid cores, and thus can be killed with conventional weapons. The longer a hashmallim faces a specific threat, the more it's spawn will be tailored to fight that threat. In the Universal Era, this means that hashmallim spawn are shaped like fighters and warstrider mecha.
The Guana from Knights of Sidonia are the primary inspiration for the Hashmallim level outer gods. They are also very 'gloppy' slinging off bits of themselves all of the time, and thus are likely the prime offenders for casting off larvae of the outer gods
I have seen an ophanim once, and it is something I never hope to repeat. To see one of them is to see the divine, to see it for what it is, and know, to absolutely know, that the entirety of human science is meaningless. To completely understand that all human religion has been nothing but bedtime stories for children. To see an outer god, to see something that we cannot face, cannot fight, absolutely cannot fathom, is to know how utterly insignificant humanity is. The closest ophanim to Earth is over a thousand light years away, and it's far too close. We watched in horror as it came from the direction of Sagittarius. The system was overrun with hashmallim, hundreds of them. It dwarfed them, it had to be a thousand kilometers across, a large moon, but alive. It tore the Hashmallim apart, it ate them. They fought back with claws and fire, their plastic bodies emulating the flat disc shape of the ophanim. Over the course of three weeks, it hunted down almost all of the Hashmallim in the system, and then it went into a quiet orbit around the star. We watched as the surviving Hashmallim fled the system, scattering.
It's terrifying to consider, but there could be one of these monsters sleeping in Sol's gravity well, since nothing else keeps the horrors running like one of them.
In the Christian Bible there are accounts of angels who are burning wheels, or made or rings turning inside of rings. This is patently terrifying as this is an apt description of the Ophanim. They are most commonly wheels or rings, covered with eyes that are tens of meters or even hundreds of meters wide. At their center there are mouths, and other alien structures and organs, and they are simply massive. An 'average' ophanim is going to be 80 to100 kilometers wide, while an exceptional alien god could easily be the size of a moon. Humanity to an Ophanim is the same as comparing an intestinal bacteria to a human being, there is so much difference between the two that there is never going to be any sort of intellectual connection.
Physically the Ophanim are best represented by the Angels Sahaquiel, Arael, and Armisael from Neon Genesis Evangelion, just increased in size several magnitude. Should an ophanim decide to come visit earth, no level of mecha is going to be able to stop them.
The Chayoth have never been encountered in their unimaginable immensity. The only knowledge of them comes from the writings and records found deeper in the galaxy, of civilizations that encountered them, and didn't survive. The Chayoth are to the Ophanim what the Ophanim are the humans, gods to the gods. It is suspected that all the magnitudes of outer gods are bound to the galaxies they are found in, and that they cannot cross the empty vastness of space between the galaxies. For the Chayoth, moving from galaxy to galaxy is a matter of no great concern.
From the records recovered, to see the Chayoth, to become aware of them, is doom. Seeing one invites it to destroy the civilization of the viewer. They are the mad gods at the center of the galaxy, basking in the glory and fire of the super massive black holes, caressing quasars, and shuddering with ecstasy in the gravity of magnetars.
The Chayoth are the gods of the Lovecraft mythos. Not Cthulhu or the Great Old Ones, but Azazoth, Yog-Sothoth, Shub-Niggurath, and the rest. (Nyarlathotep isn't in this level, it is much weaker in comparison)
Author's Note: The Outer Gods are speculative fiction from the setting of the Cosmic Era, where the outer gods that shed the larvae are from. It is written from a futuristic perspective, a projected Universal Era where humanity survived the dangers of arcanotechnology and flirting with cosmic powers not meant for man. This is not indicative of humanity actually surviving the powers it is messing with.