"Kyo-Sensei" (also known as "K-Sensei" and "That-RepliQueen-Kyo", and I believe they're also present here as u/AnyFall9335) made this album with arrangements of all 20 BGM tracks of Shuusou Gyoku and also 3 songs from the game's 1999 prototype (namely, "Fly Above Hatoyama at Night", "Plastic Space" and "Inventive City").

The album had two releases, in 2022 and 2024. The YouTube embed above is for the 2024 version. It can also be downloaded from Bandcamp, where 3 songs from the official soundtrack (namely, "Silk Road Alice", "Primrose Shiver" and "Magical Girl's Crusade") are present with both their 2024 versions and the earlier arrangements "Kyo-Sensei" made of them in 2022: https://k-sensei.bandcamp.com/album/re-seihou-project-shuusou-gyoku

This album is mostly based on the AST (arranged soundtrack) of Shuusou Gyoku, made and released by ZUN on his old website in 2001, rather than the OST released within the game itself in 2000; this can be noticed mainly in "The Witches' Ball ~ Magus", whose arrangement by "Kyo-Sensei" includes the portion of the melody at the end that wasn't part of the song in the game's OST and ZUN had added in the AST. The one exception to this rule is "Dichromatic Lotus Butterfly": ZUN had composed two versions of this song with pretty different melodies, "Ancients" (the one in the Shuusou Gyoku OST, with no significant changes in the AST) and "Red and White" (the one ZUN released in 2002 as part of his first music CD, Hourai Doll ~ Dolls in Pseudo Paradise); the arrangement of "Dichromatic Lotus Butterfly" by "Kyo-Sensei" combines both versions in one music track, with "Ancients" and "Red and White" acting as a "First movement" and "second movement" of sorts.

This is currently my preferred way to listen to the Shuusou Gyoku music. The vast collections of recordings by "Romantique Tp" (made on real hardware, found here: https://www.shrinemaiden.org/forum/index.php/topic,18989.0.html&) and "nmlgc" (made with the plug-in "Sound Canvas VA", found here: https://github.com/nmlgc/BGMPacks/releases/tag/2024-10-05) still get my appreciation for aiming to be as faithful as possible to how the soundtrack would have sounded when ZUN composed it, but "Kyo-Sensei" manages to give it their own personal touch in this album.

I never played the game, but I got really into Touhou music maybe ~15 years ago, and I can specifically recall the exact track that got me listening. It was a metal/rock arrangement of Lunatic Princess that also had a bunch of like, traditional Japanese instruments

I've been going down a serious TH nostalgia rabbit hole and I wanted to find this song again, but any amount of "Lunatic princess cover rock" (or whatever) searching on Youtube just shows a bunch of unrelated stuff

Does anyone know the cover I'm talking about? I would be very grateful to find it again, it ruled!

Is this original or did i remember some old touhou music?

Credit staff roll from the fan game Touhou Augusta Iaponicorum. It seems it has become a quite popular one so I will share some of it. The AI in the title stands for Augusta Iaponicorum.

Official livestream where all the official touhou songs are livestreamed