A variety of abyssal monster that lurks deep underground where light doesn't reach. The illustration depicts a married individual, and an unmarried individual would appear like a female that gives a sharp impression with only four spider legs growing on her back. They do not stray outside their own territory and are focused intently on continuously building a spiderweb ad infinitum, but sometimes, human men who will become their prey show up underground, as if lured by something, and finally manage to reach them.
The venom that flows inside their body adversely affects even their own spirit, making them depressed, and so they are constantly irritated. For that reason, when a man with a peculiar mentality is sexually aroused by their appearance, as if to vent their irritation, they react in a manner unbecoming of a monster and hurl abusive language at him such as "lowest scum", and will attempt to bite and inject him with venom. The effect of the venom in a man doesn't cause irritation, instead it incited wicked carnal desire towards the little girl in front of him. A man's spirit will become depressed, and a change will come over him so that he'll have no qualms about shutting them up by screwing his penis inside their mouth, the source of the abusive language, or pinning them down on the ground and violating their tiny body to his own desire.
While having sex with them like that, the man will experience a burning sensation inside his own body, and before he knows it, he'll have changed from human form into an ominous huge spider form. The huge spider has a reproductive pouch with countless wiggling tentacles around the bottom of his cephalon; furthermore, he will make the foul-mouthed little girl's body sink inside there and cover her in tentacles. All of the tentacles are endowed with erotic sensitivity and a sense of taste to relish her body, and semen will be released from every one of them to impregnate her; they will be screwed inside every single one of her orifices, and her whole body will be completely stained cloudy white.
Additionally, irritated by her insults, the huge spider will bite her body, and directly inject a bodily fluid through his fangs that contains a high concentration of the man's mana which will mix with her blood and violate her body from the inside, continuously providing her with irresistible pleasure; she'll convulse, constantly climaxing over and over, and each additional thrust of a tentacle will yield another climax. During this, her abusive voice will fall silent, and instead, she'll just keep uttering sweet words and apologies for her insults. This is because she is expressing her original personality after having the venom that was adversely affecting her spirit neutralized by the man's mana. Only when their body is filled with their husband's mana is their heart able to feel at ease. When their husband's mana that was poured inside their body weakens, and their venom gets stronger, they'll once again hurl severe insults at their husband, inciting him to bite and violate her again.
Once they've obtained a husband who serves as half of their own body in this manner, they constantly spend their time inside the reproductive pouch, absorbed in the work of expanding the couple's love nest by earnestly spinning thread while having intercourse with their husband. It's said that as long as this is not interrupted, they won't take any interest in any person other than their husband.
There's a legend that says when this web is completed, the world will enter a time of destruction, but according to another theory, the web is a giant magic circle, and when complete, the entire surface area existing above it will be transformed into an abyssal mamono realm, and all the humans will transform into their minions.
As expected, the appearance of unmarried and married individuals differs greatly, and the illustration is of a married individual in a state of being joined with her husband. They have venom and will spew venom such as “You're the lowest scum!” at men, which is rare for a monster girl.
By the way, their husband is able to freely return to human form, and supposedly they also have sex while he's in human form as well, but for some reason, they're shy about being seen getting it on with their husband in human form or something to that effect.
Concept: "Cthulhu", "Monster rape" (the term used is 異種姦, which is pretty much the japanese term for the genre of girls getting fucked by monsters), "Venom-spitting loli", "Ominous and cool"
This time, it's the girl with a venomous spirit, constantly getting fucked by a giant spider, "Atlach-Nacha".
A common theme of the Cthulhu inspired girls is the husband's transformation into an inhuman form (though he can freely return back into a human). When they are connected with their husbands, they begin to resemble their original appearance. This time, it's a loli-ish girl incorporated into a giant spider, and getting fucked non-stop. Rather than the giant spider, it's the little girl that's venomous, and by uttering venomous words and phrases she'll make herself get fucked.
With this kind of extreme design and ecology, she's almost poisoning the Encyclopedia itself! While in the profile text you're supposed to read their phrases like "You are the lowest scum.", when they're husband and wife, it really kinda sounds more like "You're the lowest scum… <3"
In the original mythos, the Atlach-Nacha is a terrifying spider deity, lurking deep underground and eternally spinning its webs and creating its nests, unforgiving of anyone who dares disturb its work. Other than that, it doesn't seem to have any other interests or motivations. When this nest is completed, legend has it that it will bring about the end times. In the encyclopedia's world, the "end of the human world" means monsterization and transformation of the land into a demon realm, of course.
In the encyclopedia's world, only the ground immediately above their nests would turn into a demon realm, but suppose that they lived underground across the entire world, and their nests covered the entire globe, really the entire world would turn into a demon realm… Since the other Cthulhu based loli, the Wendigo, has a mostly white color scheme, based on the idea that the Atlach-Nacha should be a "darker" little girl, her colors are mostly black and a poisonous purple, with red lights to really stand out.
A common motif of the Cthulhu girls are "cracks" in their tentacles with shining spheres in them, but the hard parts here like the spider's shell, legs and fangs still have a sort of slimy tentacle-ish image to them.
In contrast to the Wendigo's long white hair, she has long black hair. And while the Wendigo would have an almost demure air to her while "indulging", the Atlach-Nacha would put up a strong front… (Of course, both of them would be at the mercy of their husbands pounding them from behind either way)
Regardless of their appearance as a couple, the Atlach-Nacha by herself has the appearance of a human girl with spider legs growing out of her back, with luminous orbs arranged in the pattern of an arachne's compound eyes.
Though compared to an Arachne her design is pretty tame and close to a human, the intention is to have a stark contrast between the wife's appearance and the husband's by lowering the amount of monstrous features on her.
Her slutty clothes don't hide anything at all, and she's basically completely bare. Her fair, bare skin is supposed to contrast the surrounding dark purple tones. (Of course, the main reason is that I love slutty clothing!)
Her sleeves are like a kimono's. By making the arms kind of disappear into the surrounding blackness, it makes her torso stand out even more.
I consider the chest accessory just something she has in common with the Wendigo. Hers has a design combining a spider and a tentacle creature.
The joints of her legs have bushy hair of a poisonous purple color growing from them. There's lots of hairy spiders out there, so I went for that sort of look.
(as an aside, I don't really get why you'd have to have a contrast between the girl and the husband? when she's single she's just going to look like a standard loli to you, when you're all spidered up you ARE the spider so you don't really care about how her body looks in contrast to yours, and seeing her "complete" it doesn't really matter if you find the contrast between the two appealing because she's already taken at that point, so what's the deal? I mean it would have worked if the spider part was some kind of magical construct or something.)
It's kind of hard to see what her husband is supposed to look like from the angle in the illustration, so I drew a few sideways angles in the sketches too.
The part filled with countless tentacles that the wife is drawn into is a "reproductive pouch", rather than a mouth.
Even the part that looks like a tongue is just another tentacle (but the husband can still "taste" his wife, of course)
The real mouth is hidden behind her back, above the reproductive part.
On the left and right sides of her waist are the husband's fangs, and the thin purple part surrounding the tentacles outside is his chin.
Spiders tend to have large, rounded silhouettes with huge heads when viewed from the front, so to give the spider a kind of "ominous, villainous coolness" instead of it looking goofy and silly, I spent a lot of time considering angles and placement of parts, and what sort of silhouette would result from it.
By the way, the husband and wife each have 4 legs. Together as a couple, that makes eight, symbolizing how they've grown closer to her original appearance together. And yeah, their proof of intercourse is just dripping all over the place… Please understand.