May I Introduce Mr. Eldritch Abomination, and His Friends · 3:26am Feb 7th, 2013
Making this a blog post, because it became too damned huge for me to feel comfortable posting it in this forum thread, and I wasn't sure the in-universe format was appropriate.
This is from a speculative fic that I've been slowly formulating. I've had vague ideas about the antagonists of the story, but I decided to take the opportunity to flesh things out a bit. I guess such a report as outlined below would come from far in the future of when my planned story takes place, when these horrors are just being discovered...no real plans to write anything else in this far-future time period, but who knows? Writing in-universe because I figure it's good practice for when I try to actually get this story moving... If anyone bothers to read this infoblob, any feedback/criticism would be welcome. 
Fleet Intelligence - Threat Report - Classified XK Level 0 (Eyes Only, No Headware Storage)
Accessed 734 AS, Terminal 4, Officers' Library,
HBS Abiding Peace, Flagship of The Fleet of Her Eternal Benevolence
Name: The Calm
Type: Life-consuming, intelligence-preferential Eldritch abomination
Origin: Unknown
Weaknesses: Sol-class or greater focused-balefire weaponry (Eternals be Praised)
Offensive Capabilities: Known weaponry is based on atomic-bond shattering
Description: The Calm is the explanation for The Fermi Paradox. They appear as matte-black tentacled forms, the smallest of which can destroy a Triton-class orbital habitat (max. pop. 50 million) in approximately 10 minutes. The number and apparent size of a given entity's tentacles appears to be entirely fungible. Any and all organic material--shielded or not--coming within a 25-meter range of any part of an entity disappears--consumed through unknown means--leaving no detectable traces. The largest specimens recorded were easily capable of dismantling an Earth-sized planet, though they appear to have some aversion to the complete destruction of planets.
Despite appearing to have measurable girth, the tentacles act as monatomic lines, never seeming to physically strike their targets. Where the tentacles pass through inorganic materials, all inter-atomic bonds are left shattered, and are temporarily prevented from reformation by unknown forces. All weaponry save concentrated Sol-class fire is absorbed by the entity's skin, leaving no noticeable damage. Under no circumstances have any entities shown any reaction to attempts at communication, nor any less-than-rote reaction to attack--thus leading to their moniker. Ineffective attacks will be ignored, damaging attacks will be retaliated against until the entity is sufficiently deconstructed so as to be rendered useless. Any piece of an entity which is too small to effectively attack will disintegrate within approximately 30 seconds, leaving no trace, but until such time the piece is still instantly deadly to any organic life within 25 meters. All scans run on active entities or disintegrating pieces have been inconclusive, save those which allowed The Eternals (may our prayers bring them warmth) to develop balefire weaponry.
After centuries of dealing with The Calm, we have come to understand something of their behavior, though nothing of their motivation or purpose. They apparently react to the presence of intelligent organic life of any sort, but the higher the aggregate intelligence in both achievement and multiplicity, the greater the probability of an attack. Artificial Intelligences do not draw their attention until they reach approximately S2-level transapiency. Their eventual detection and consumption of powerful AIs implies some ability to sense actual levels of raw information processing--this has yet to be explained.
Attacks are swift and deadly, but some limit to their resources is presumed, due to a weak statistical proportionality of their response to total regional intelligence levels. Despite vast cluster-wide surveillance networks, the origin of The Calm remains a complete unknown; thus, some sort of transdimensional nature--beyond even the current understanding of The Eternals (may our service yield them strength anew)--is now assumed. Fleet standing orders recommend a minimum 10:1 raw superiority for any planned confrontations, with the minimum superiority yielding an expected 20-30% losses. See attached documents for guidelines regarding maximum population densities and technological levels, as well as recommended colonial region scattering, defense patterns, and emergency fallback scenarios.
End report. Purging buffers. Scanning headware...3% optical hardware passive retention detected, please stand by for purging...complete. Security protocols complete. Doors unlocked.
Have a blessed evening. May Her Light guide our way to the future.
It's interesting to say the least. I didn't really understand the purpose behind the "Triton-class" stuff. Nice abomination nonetheless.
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Oh, just a random name, really (named after Neptune's moon), but the overall intent was to show that The Calm is the next thing to an irresistible force of nature: a single, small entity can wipe out 50 million souls in ten minutes, just by waving its arms at them. Larger ones can dismantle entire planets. And if you don't have ten times as many ships, with
godEternal-forged weaponry, there's nothing you can do to stop it.All your people can do is run, in as many directions as possible, and hope they can't catch you all.
So terrifying...
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Fear not, my child; for the Eternals watch over us always. 
May the beacon of Her Light guide your way home, from whatever dark places you must tread.