Wikipedia links from the Touhou Project to an interesting article, called "database consumption", where people are fans of the component parts of an original work, but want nothing to do with the original work itself.
https://en.wikipedia.org/wiki/Database_consumption
It gives the example of Hatsune Miku, who strictly speaking is a fictional character attributed to a sampled singing voice in a vocal synthesizer VST called Vocaloid 2. She was the product branding. There is now a huge industry of fans inventing stories about Hatsune Miku and rendering/drawing pictures of her and enjoying thoughts of her being their waifu. Whatever they've made up is now their headcanon.
I can totally understand Hatsune Miku fans asking you to get lost if you tell them you bought Vocaloid 2, it's cramping their vibe.
Is it the same with the menagerie of Touhou characters? Are there people enjoying thoughts of Marisa Kirisame who don't want to be reminded she's a character in a shoot'em'up?