I added the Mermaid tag, because although it isn't visible in this particular image, this character is most definitely a mermaid in the actual series that she is from.
Removing mermaid tag for that exact reason. You wouldn't add the tail tag to something if it wasn't visible, even if the character is known to have them. Same logic applies to mermaid.
Your argument holds no merit for two reasons. First the Mermaids of the One Piece world have the ability to split their tails in two and thus gain the ability to walk on dry land once they reach the age of 30 years old. Hence why the Mermaid Kokoro was able to live in the city of Water 7 and Drive the Sea Train for several decades.
Additionally is the fact that your argument hinges on the assumption that because it isn't visible, it somehow isn't part of her identity. This is a logical fallacy. This woman is by definition, part of the species of the Mermaids and Mermen. Thus she has a fishes tail whether we can see it or not. If we take that part of her identity away from her, we might as well question whether this is actually even the character from One Piece in the first place.
