I am working on a fantasy short story as practice for my larger novel. The MC of this story is a character I had planned as a future Love Interest of the MC of my book, so I thought it would lend great credibility for her if they started out separate and evolved their own personalities naturally. Now the problem I am having is that I am struggling to find a creature from mythology that fits her personality as I now see it. I would love to have a pre-existing mythological creature she could be, and several almost fit her personality. Almost. I'm just worried about 'cheapening' the character by making her too different from the myth she roots from, and losing credibility in some of my audience who are familiar with the mythology, but making up a creature so similar to so many others seems like such a less preferable option. I have an Idea of the sort of thing she is: the character is a humanoid female creature (Not sure if there even are males yet of her race or order, I haven't thought that through yet), that is supposed to be wildly beautiful and seen in human culture as fairly mythical, but still mortal (thought a lot on making her immortal, but that proved too difficult to write). Options I am considering basing her on are: Nymph (the problem with them are that they are too promiscuous for her personality, and are option too powerful, like at a god-like level), Siren (Too malevolent, I fear she'd be expected to be 'evil' as a siren), and Nixie (I don't really imagine her shape-shifting and that seems to be a crux of the myth). Any other mythology leads/advice any of you can render?
Naiad? (Or oceanid, nereid, I think there's others.) They're just nymphs without the PR, really. Is she water-based, specifically?
Y'know, a friend of mine suggested that too. I'm hesitant to use any sort of nymph because of their goddess level of power they are generally given, like in Greek mythology. Like I said, I considered making this character "almost-a-deity" but that was just too hard for me to write. She is from a region with a lot of brooks, geysers and springs, so water will likely be sacred to her, yes. Do you think I could get away with making a very mortal Naiad, or would it harm her credibility with most people? Pretty much I need to know: how far away I can go from the myth, using the name, without it weakening the work?
I think it this case you'd be fine with naiad or nymph. They're definitely regarded as less-than-godly, albeit sort of god-adjacent. They can have powers but they're not as powerful as a god, they can be killed or die by other means, though they're generally considered immortal. If you wanted to err on the side of caution, maybe she could be the child of a nymph and a human, if that's a possibility in your setting? Or she could potentially just have a very long lifespan? I think I could accept a mortal nymph, myself, as long as you sold it. I might want some other nods to mythology to make up for it.
Nymphs are, in fact, mortal even in the Greek source material. They have long lives, but they do die naturally.
Have you considered making her a human/(race x) mix, that could get her close to something you wanted, but the human element could lend to making her more relateable, cap powers, and allow her to be 'like a mythical race' and also different in ways you might need.
It's a little more eastern but there is the tales of a Kitsune. They are legendary foxes that take the form of a human at night and come home to their mates, then turn back into foxes during the day and go out to play. You could obviously play with that a little as their lore is already kinda loose. The jist is that they are humanoid fox shapeshifters, often seen as fun loving and sexual (not necessarily promiscuous though). They are typically viewed as mildly immortal, only being able to die from wounds but not from age. As they get older they grow more tails and become wiser. They come from eastern mythology that does have geysers and hot springs. I would do some background research on them if I were you. From what you describe I think they would be a good option.
