If you're referring to something like "Elf ni Imouto o Tsukeru Hon" (which translates roughly to "The Book to Give to My Little Sister the Elf"), it's a Japanese adult visual novel and manga series that has been adapted into an anime. The content you're asking about seems to relate to adult themes, given the nature of the title and the request.
Have you seen this OVA? What’s your take on dark fantasy corruption anime? Let me know in the comments below. elf ni inmon o tsukeru hon the animation full