The sci-fi fandom has a lot of nonhuman characters and personas who are anthropomorphic in that they have any number of human-like traits (walking upright, speech, thought, civilization, technology, hands, etc.) yet they are not Earth animals. Very common would be alien species, which would be species of animals that are not human and also not Earthly creatures as is found in the furry fandom. It would be easy to write a fictional world where it's a planet that isn't Earth, and there are creatures that are like fairies or mermaids (or furry characters, for that matter). However, you will find a lot of overlap since the furry fandom is an offshoot of the sci-fi fandom. I'm not sure if the sci-fi fandom includes fairies or mermaids, or if that would be more in the fantasy fandom. But there again, you'll find a lot of similarities and overlap between the fantasy fandom and the furry fandom because furry characters and fiction are a form of fantasy. A lot of furry artists draw fairy characters or mermaid characters (whether they have a human-like form as fairies and mermaids are traditionally drawn, or have an anthro animal-like form). That's the great thing about all the fantasy genres; the creativity and imagination is limitless.