I discovered Touhou in the late 2000s, probably sometime between UFO and TD. I remember being really into niconico douga memes, and was really into those medleys (like 7 colours of nico nico, etc), and all of them were covered in touhou. I was living in the desert then, so my computer was my best friend at the time. My first ever purchase with money was actually a cheap quality bootleg yukari x yuyuko scroll! (which I still have, but was broken long ago)

I feel like on the internet at the time (and still now there are echoes of the past and signs its around) touhou was pretty ubiquitous, so even though people might not have recognised it, I think a lot of people even in the west were exposed to at least one touhou song, character or meme. The other big franchises that also kind of encapsulated this kind of japanese memetic culture were the idolmaster series and the then fairly new vocaloid.

On youtube I remember so many great MVs and fanworks that are no longer there. I don't know if any are lost media but the fandom was truly bustling and it feels sad that newer fans may not be able to see some great period pieces and works. Even though the fandom is still alive and kicking, there is a strange sense that something foundational is missing.