The popularity of the Touhou Project according to Google Trends, for both the Eastern and Western fanbases.
It’s actually kind of interesting to see how the popularity grew. It didn’t actually kick off in the West until PoFV, and even then it didn’t get really popular until UFO. DDC was the most hyped game in the Western fandom, and UFO was the most hyped game in the Eastern fandom.
It looks like Touhou has always been relatively popular in Japan but in the West it came as a sudden surge of popularity (and also appears to be declining again, oh no….)
(Note: The graphs aren’t to scale, Touhou has always been significantly more popular in the East. Also, Google isn’t as big in Japan as it is in Western countries, so the data might not be that accurate. I just thought it was cool.)