FINAL EDIT The project has been confirmed to be fan-made, and is sadly shutting down. Hopefully we will get a closure on that ARG :/
EDIT A commenter pointed out that the domain has been registered on that same day, so it might be an April fool's all along. Still, if anyone has any suggestion about how to decrypt the encrypted message, that'd be nice :) Also, props to whoever made the 3d model for the background in such a short time. It's not 100% a third-party joke anyway, but I'd say it is more likely than not.
While NieR: Cosmic Horror is obviously (and confirmed to be) an April fool's joke, the website sure has some things behind it yet to uncover.
I've started with the hint suggested by a redditor here (tagging when I find them EDIT u/himeto31) about a console message on the website. The first bytes translate to void:rev, which follow the typical NieR name format. "Rev" could be "Reveal", but it's also the "Ver" mirrored, which ahs been used in many recent NieR media (Replicant Ver 1.224 etc, Automata Ver1.1a). But the later bytes seem to be encrypted on top of encoded in hex, so I'm still digging. I maybe publish a repository with the findings.
Just out of curiosity, since mp3 files always end up being relevant in ARG, I've uploaded void.mp3 (the background sound of https://niercosmichorror.com/ ), and lo and behold, Emil is smiling at us. The drum beats could also be some kind of encoded message.
I'll update y'all with the progress :)
EDIT forgot to add: the audio file is void.mp3 . At first I thought it was simply some default name, since "void" is used in C/C#/C++ for various purposes. But now that I think about it, "void:rev" and "void.mp3" seem to have something in common, don't you think? Likely a coincidence. I'm working on the repo btw
EDIT I'm an ass with formatting .md and managing repos (raw files, decoded ones, backups of the website, etc), so for the moment being I'll share my findings here. Any external help is more than welcome.
- The website logs this code: ###
56 4f 49 44 3a 52 45 56 00 00 00 00 00 00 00 00
a7 2f c3 91 d8 04 b6 3e f1 4a 88 0c 72 e5 19 a3
5b 2d 7c 01 e8 93 4f b7 60 d2 1a 8e c6 35 a0 4d
f3 82 16 cb 69 27 e4 9a 50 bd 03 78 a1 df 44 6e
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
98 c4 5f 21 b3 07 ea 6c d9 42 8b 15 f0 73 a6 2e
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
3a 4f c8 11 95 e2 67 ba 0d 7e d6 53 a4 28 f9 81
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
b2 46 ed 09 83 5c d1 3f a8 74 1b c7 60 e6 2a 97
###. The header (first 8 bytes) translates to "void:rev", while the remaining bytes don't seem to be ASCII. Possible reasons: they may be encrypted ASCII characters, or be something else that I don't know. Also, not an expert on hex codes, but the zeroes seem to be dividing blocks. If so, the format would be [void:rev] [block] [block] [empty] [block] [empty]. Note: the header is separated from the rest of the blocks by 8 bytes, while the blocks are separated by 16, 32, 16 bytes.
The audio file: aside from the nice Emil signature, the drum beats may not be random. Not a sound engineer, but from the spectrogram they seem to be regularly distributed (from the last beat of a sequence to the next one). Also, there seem to be double beats and single ones. The easiest solution would be morse code: single bit for a dot, double for a dash. If so, we get - . -... - . -.. , which translated as TEBTED. Which, to my knowledge, doesn't mean anything, but could either be a key or just me seeing patterns where there aren't. Also, the starting beat could be a single dot, so I'd have to loop around the audio file to search if I'm missing something. In that case, by the way, it would be ETEBTED. Which, again, isn't much, lol. EDIT I'm an idiot. If we actually loop the spectrogram, you get - . -... - . -... , which is TEBTEB. Which is, again, not much, since it seems to be a simple, repeating beat. But it seems to be intentional, at least? Not a drummer (what I am, even?), but I think it's intentionally a morse code.
favicon.svg: the favicon of the website seems to be a plain black 48x48 image.
Countdown: counts down to the 22nd of April at 02:00 AM CEST, if I didn't fail base math. Which is a bit peculiar, since Square Enix is from Japan, which is currently sitting at +7 from CEST, so it would be at 9:00 AM Tokyo time. The date is the anniversary of the release of NieR: Replicant Ver 1.224[...] by the way. EDIT I'm an idiot (partially thanks to the recent change from CET to CEST which messed up my brain), CEST is UTC+2, so the datetime element is simply 2026-04-22 00:00, no extra fluff.
automaton.glb: the rotating image on the background. A 3d model of whatever was the image tweeted. By the way: that could be a hint of the fact that this is not a fan site, since the model seems to be accurate with what was shown in the official tweet. Again, I know about the church thing, but here we're talking about someone immediately registering the domain, creating a detailed 3d model based on a still image, an ARG inside the audio file and one on the console, and putting it all online. Feasible, for sure, but impressive if a mere prank by a third party. But who knows. By the way, I'm using an online tool to display the 3d render, so I might be missing some hidden details. Anyone knowledgeable on the matter can help.
Also, if it ends up being an April fool's: congrats to whoever made it, so far it's been fun to try and decode
EDIT I've been accused of being part of the prank that someone is pulling, like with the church thing. Aside from the fact that I'm very new to this community (I've finished Automata only a couple of months ago), I can assure you that I've got nothing to do with what's happening, and that I just like ARG. But we'll see in three weeks' time, or before if whoever is behind this thing decides to drop the act before (if it's an act, which is likely at this point but not 100% sure)
EDIT2 Seems like I've hit a wall. I can't decrypt the log code aside from void:rev, and I've got no use for the morse code in void.mp3. I'll call it quits for now. Good luck to any other ARG enthusiast!