It looks like you’re referencing a Japanese title: ( Erufu ni inmon o tsukeru hon 1 ) Which roughly translates to: “Book 1: How to Apply a Corrupting/Curse Mark on an Elf.”
Elf ni Inmon o Tsukeru Hon 1 is a definitive example of niche fantasy erotica done right. It understands its audience perfectly, combining the exotic allure of elven characters with the taboo thrill of magical body modification. elf ni inmon o tsukeru hon 1