Also known as the temptress or the seductress, the vamp is one of the more dangerous characters the hero meets on his journey. A devastating beauty who is as evil as she is sexy, she uses her feminine wiles to exploit men’s flaws to her own advantage. If the hero falls for her, he will be destroyed.
Unlike the femme fatale, her more neutral counterpart, she is completely evil and cannot be redeemed. This is because her role in the story demands it. She generally makes her first appearance in the initiation phase of the hero’s journey, after the hero sets out on the adventure but before he masters the unfamiliar world. In many cases, she represents a leave your quest test or a secret test of character.
Joseph Campbell thought this character was so important that he dedicated an entire phase of the monomyth to her:
When it suddenly dawns on us…that everything we think or do is necessarily tainted with the odor of the flesh, then, not uncommonly, there is experienced a moment of revulsion: life, the acts of life, the organs of life, woman in particular as the great symbol of life, become intolerable to the pure, the pure, pure soul. The seeker of the life beyond life must press beyond (the woman), surpass the temptations of her call, and soar to the immaculate ether beyond.
As such, the vamp represents the more carnal elements of the hero’s nature, which he must reject or overcome in order to be transformed. Confronting her is an important part of the story because it gives him an opportunity to recognize his flaws and master them. It isn’t easy, though–the vamp is an extremely deceptive character, and often plays tricks like the wounded gazelle gambit to confuse the hero and gain his sympathy.
While often a female character, there are a few male examples of this character. Mr. Wickham from Pride and Prejudice is one of the more obvious ones. Basically, the vamp can be of any gender, so long as s/he is someone the main character finds sexually enticing. Because of the traditionally male-centric nature of the hero’s journey, however, she’s almost always female.
Also, I think it’s important to add that it’s not just the vamp’s sexiness that makes her evil, it’s the way that she uses it to manipulate and undermine the hero. If she starts out evil but has a heel-face turn later in the story, she doesn’t fulfill this trope. Likewise, if falling for her wouldn’t make the hero fail, then she doesn’t fulfill the trope either.
I’ve played with this trope a little bit in my own work, but not in a big way yet. Heloise from Star Wanderers: Fidelity (Part II) probably fits this trope the best, though her appearance is fairly brief. Tamu from Bringing Stella Home might appear superficially to be one, but she’s actually more of a fair weather mentor for Stella (and has good reasons for choosing the life of a Hameji consort). And of course, Mira from Desert Stars doesn’t fit this trope at all, seeing how much she changes by the end.