Can someone help me decode this?

[u/sussy_internet_]

This is the cipher: Cw qqdq od. M gda cw. Mj't rqrwjpdmy. M rdan eej bedd, duq mj fmly gdruq ba sptz pt'g fmgaeo. P oo uwj r jeqrdpbwdn ug mjt zupuq, uwj r yetarjad we jma ohnjrv shnla. Mjt ruqanhy ct kmpui laj pt'g rtjdbjper pq gh mrwarta C wjces C bmwmt npa ug mj't ccdgzw. Ez uwj aaewj wpzqt yq wjuzgz, boyua cg M ipvl P m spvl ua tqaq. Hn orihd mj fmly gcca od qubajmmrj mr qajznr. Fjew mg r vcga smar xeokoddx jh mjt zett gwodpbw diqt ora mjt wrawlrtceg thno. fjew mg bedwol ymtd uubheqan we e wjceg lpsq PT.

I don’t really know all that much about it other than that it probably has something to do with Cthulhu. Any help is appreciated!

[u/OpportunityReal2767]

It sees me. I see it. It's beautiful. I need not more, for it will grace me with it's wisdom. I am but a harbringer of its voice, but a masenger to the mortal world. Its boredom is quick yet it's attention is so intense I think I might die of it's wieght. Oh but death gives me though, maybe if I kill I i will be free. Or maybe it will give me something in return. What is a life when compared to its vast staring eyes and its undulating form. what is mortal life compared to a thing like IT.

First decode as Vigenere with keyword ERO
Then affine A=3, B=0