If your friend is some masculine sigma person, it could be a problem. My suggestions are: Have a chit-chat about Rinnosuke, or maybe the fact that they are using interesting Myths such as Youkai's, Chinese Legends, Greek Gods, and so much more. Touhou isn't about the girls and feminism, it is more about the story (Manga, check out the Three Fairies of Light) and is very entertaining especially those Doujins and games (Fan/non-fan).
Unless it's a girl we are talking about, it won't be that easy too.
In my experience, the Girl's genre is more romantic when reading Webcomics or manga. Like the (fake/extrovert/son of a bitch/cheater) emo girl I had last year, she likes anime and Manhua and other romantic stuff (Especially porn), like Boys fucking gay love. I tried to convince her to like and be part of the Touhou community and she said yes, but guess what happened in months? Still following other stuff, (like Genshin).
Another example is my friend, who is so nice to every single one in school. She always shares her thoughts about the STRAIGHT romance in each of her readings, sometimes it makes her mad. So the shortcut here is, romance with a handsome Korean-looking guy, I'm not trying to be against it, okay?
But as we speak about Touhou. You are lucky if your friend is more of a slice of life, fiction, action, entertainment, anime, interesting stories, and mythological scenarios, then Touhou is the answer they are looking for. You can say Touhou is not an anime, just in case.
Now again, Touhou is more about the facts and stories. Tell them how you feel and how it is convincing. And the big shot through the heart... is Osana Reimu.
