I should be ashamed of myself, Tohou is a long running series of bullet-hell games https://en.wikipedia.org/wiki/Touhou_Project
And vocaloid is a voice synthesizer that was developed not all that long ago https://en.wikipedia.org/wiki/Vocaloid
I just wanted to point out the main thing that's amazing about Touhou. It's kind of funny too:
following the release of Perfect Cherry Blossom; seven circles sold Touhou derivative works at Comiket 65 in December 2003. At the Comiket 74 in August 2008, a total of 885 circles had Touhou derivative works on display or for sale, out of a total of 35,000 circles participating at Comiket.[37][38] At Comiket 77 (December 2009), 2,372 circles were dedicated to Touhou, breaking the previous record held by The Prince of Tennis at Comiket 66 (August 2004), which had 2,130 circles.[39] At Comiket 85 (December 2013), Touhou was still in the lead, with 2,272 participating circles selling Touhou derivatives, far outpacing those of other franchises.
So, you have the main series of games, which itself got a Guinness world record for being the most prolific shooter series made by one person. But on top of that he's managed to somehow spawn a media empire that consists of over
2300 separate groups who make commerical fan-art of his stuff. This includes e.g. possibly
hundreds of different musical groups of various genres from electronic to metal who cover his game's music. This whole phenomena actually became an issue at Comiket (Japan's huge fan manga expo) since they were taking up so many of the total stalls, and creators based on other series started to get the shits.
So ... basically a lot of people "into" touhou are into all the various related media and most of them don't actually play the games now: it's big enough that it's an actual subculture and the games are just one small part of the avaialable media in that subculture. Seriously, it's pretty goddamn amusing that one guy making games in his bedroom managed to spawn all this.