Five Figure Fanwork Exchange

Open to discussion, but could I check I understand the purpose of having it as a separate fandom? If they only appear in that book, I understand that someone could offer and request that relationship and be confident that that's all they need to know - is that correct or am I missing something? (I could also reflect that in the relationship label, similar to how some of the Supernatural relationships have episode tags to help people remember where a particular character is from.)