The little mermaid story got flipped completely, didn't it? Modern mermaid romances seem fascinated with the idea of captivity and freedom, but it's less about the human wanting to be a mermaid now and more about the mermaid being forced to navigate our world. You get a lot of 'fish out of water' humor, obviously, but layered with a real tension about autonomy. Is she a curiosity, a prisoner, or a willing participant in this surface-world relationship? There's often an ecological angle creeping in too—maybe her people are under threat from pollution or overfishing, and the romance is tangled up with saving her home. I find the ones that lean into the inherent tragedy of the original more interesting, where the magical cost of legs is actually painful or the cultural divide feels genuinely insurmountable.
That forbidden love element is basically the engine of the whole subgenre. It's not just human vs. merfolk politics; it's about two completely different biologies and social structures trying to mesh. The logistics alone are a nightmare, which writers have fun with. How do you hide a tail? Where do you keep a being that needs saltwater? The romance becomes a problem-solving exercise in trust and adaptation, which can be oddly sweet. But I've also read a few where the mermaid is the predator, not the prey, and that power shift is refreshing. She's the ancient, dangerous creature, and the human is the one out of their depth.