Let me first say that I'm new to byuu- so it's possible some of this is old hat, but at the time the search on here was broken and I wasn't able to find any of the following things just by looking through the original thread.
His FA account and fursona was documented there, but no mention of a DeviantArt, so I decided to snoop around DeviantArt and see if there was any evidence of an old abandoned account, or an empty account with only a favorites gallery or some such that could have belonged to him.
This first finding was obviously
our bwuu:

It's too cursed for me to download, but bwuu's e621 ref sheet (see page 3 of his thread) sports the same 207 dog tag, and both feature the other character 'fwo'.
This one, not so sure as it doesn't resemble his fursona as much:

Hoping to find a dead/shadow account for byuu, I pulled the names of every user who liked both of these posts and cross-referenced it with all the likes on every piece of Bahamut Lagoon fanart on DA (there isn't much of it) but did not find any overlap whatsoever. I also kept an eye on the comments section for all these pieces to see if there was anyone who was particularly obsessive about the game. Deleted accounts still appear to some extent, including on like lists, so even if the account was deleted it could still theoretically be found.
At one point, I almost thought I found someone that could have been a young byuu. They were the most active on all the Bahamut Lagoon stuff, they had written a review of Terranigma on GameFAQS in 2005 (seems byuu made a soundchip thing for the game or something), and also mentioned they deleted their old account even earlier on. However, when I looked back into the comments on their page, I saw two friends congratulating them for getting into JHU in 2008. From what I understand, byuu would have been 25 in 2008 so that doesn't seem to make any sense. Oh well, dead end. The account name was nepheliad in case anyone is wondering, though.
After that, I just spent a bit of time searching stuff like 'higan', 'byuuhigan', and so on because I feel it's impossible for someone like him to never have been on DA in some capacity.
First is the only post from this account 'byuuhigan', screenshot from an article about him written in 2011 but posted in January, 2020. This account is otherwise empty. There are no favorites. The reason this weirds me out is because for a long time DeviantArt has offered a free service where users can privately host up to 2GB of images. So why make an account to back up a picture of an article from 9 years ago, and why not just take advantage of the private hosting feature if all you're doing is archiving it for yourself? Idk,
but here it is:
There's one more thing I found which is equally strange, and my point about the private hosting still stands here. This is a person who has posted nothing but the same three screencaps of some very technical looking byuu tweets to both DeviantArt and Imgur.
Again, no favorites or anything:

The account name is kamijee1990. The other thing that turned up from that username is this,
a Wattpad account called 'assetfinance' that is connected by the kami jee name.

This might not be useful to begin with so I'll call it a wrap here, but I was thinking it may be possible this person collaborated with Near or something at some point and that it could reveal some clues to whatever identity he was going by in Japan, or something like that. I looked into it initially because the DeviantArt posts seemed like a 'note to self' kind of thing, which made me wonder if it could be byuu but I don't think he would leave such a trail of information.
I hope that this was an entertaining read at the very least, like I said because I'm not an expert on this guy I thought these posts may make sense to someone more familiar than myself.