https://mangakatana.com/manga/oomuroke.2711/c88
Supposedly the book is a horror manga with a cute cover. The actual content isn’t ever shown unless they cover it in a different chapter.
I haven’t actually read the series outside of this one chapter, so there could be a larger context I’m missing.
Both characters get a lot of memes/attention in these kind of communities, so they’re expected to be well known if you’ve been otherwise active here (or in any anime group).
For example, I haven’t watched either show, but I know that the green haired girl is Übel from Frieren and the wolf girl is Horo from Spice & Wolf.