CLAMP's legacy as originally starting from doujinshi circles is really fascinating and makes a lot of sense when you understand that a lot of their manga are just straight up loose adaptations or spiritual reinterpretations of some of the most iconic pieces of 20th century japanese fiction, especially literature.
In many ways a lot of their storytelling is best described as "derivative" but I don't really like using that word because it has such a negative connotation. I think CLAMP's genius is actually their ability to iterate on the themes and ideas and character types and other inspirations that they derive from, especially in their ability to translate those elements to a visual/aesthetic format and to add themes of queerness into those stories or highlight the already present elements of queerness.
Like Tokyo Babylon is inspired by Teito Monogatari (and also Peacock King but that in of itself is a subject for a whole other post). And it's not just limited to the quick one-off comedic reference to Yasunori Katō that we see in the beginning of the manga. The title itself is a reference to the first manga adaptation of the Teito Monogatari. And that title choice for the adaptation was itself probably a combination of a deliberate reference to the Book of Revelation which was culturally relevant in Japan at the time for reasons I'll explain in a little bit, as well as the fact that the author of Teito Monogatari based Katō in part on Aleister Crowley. But Teito Monogatari and Tokyo Babylon are fundamentally stories about the exact same subject matter, that is the City of Tokyo itself.
X aka X/1999 is pretty self evidently a loose adaptation of the Digital Devil Story novels, the ones that would go on to be adapted loosely into the Megami Tensei video games. An apocalyptic battle for the fate of the entire world fought in Tokyo between two ideologically opposed groups of super powered beings, one of which is literally called The 7 Angels. There is a magic sword associated with the death of a female loved one, there are references to a whole bunch of religious and occult concepts from both the east and west, and one of the key locations for the plot is an elite private high school. X and DDS/ Megaten are both quintessential examples of media born from the Japanese Occult Boom. Bad Japanese translations of the prophecies of Nostradamus in the '70s would inspire the Boom, and then would become mixed with the social and economic chaos that was the Japanese asset price bubble and other late stage capitalist nonsense like the financial collapse in the '90s is why you have in both Tokyo Babylon (and by extension the manga adaptation of Teito Monogatari) and X this weird obsession for the Book of Revelation in a ostensibly non-Christian cultural zeitgeist. Tokyo was both "Babylon" as in Rome or any sort of other hypothetical city / civilization that represented decadence and degeneration, and it was Tel Megiddo in the sense that it was the place where the end of days and the battle heralding the Apocalypse would commence.
And then Gate 7 is literally just one of dozens upon dozens of fanfic/ rip-off / adaptations of / works inspired by Makai Tensho which came out in the '60s and sort of is kind of the cultural grandfather of novels like Digital Devil Story, Teito Monogatari and the Onmyoji series. It's the modern source of basically every piece of Japanese pop culture that treats the notable historic figures of the Warring States Era as more than just badass warriors but literal demigods, sorcerers and super powered beings. Mirage of Blaze(which also has some pretty clear inspirations from Tokyo Babylon and it sort of exists in a trifecta with TB and Yami no Matsuei in their relation to the Onmyoji novels by Baku Yumemakura but again, that is the subject for another post), Samurai Warriors and Sengoku Basara, pretty much all of the Fate series but especially the original Stay Night and especially especially Redline/ GudaGuda and Samurai Remnant, and a whole bunch of fighting games and Ninja OVA'S are all examples of Makai Tensho's influence.
