Basic Trope: The Unicorn is used as a motif representing purity, rarity, wildness and associates those around it with innocence.
Straight: The typical Unicorn and Virgin scenario - a maiden attracts a unicorn to her at some secret spot but it is attacked by evil folk who the unicorn then kills before fleeing.
Exaggerated: The unicorn is a creature that is so good, pure, and rare everything in it's presence becomes purified by just looking upon it.
Justified: Unicorns are so powerful and dangerous that nothing would dare hurt them. The lack of danger and fear makes them very trusting and evil creatures tend to avoid the places they inhabit.
Inverted: Unicorns are black coated malevolent spirits whose attractions to young girls are down to much darker impulses.
Subverted: Unicorns appear wonderful and glamorous but that's because of an actual glamour that allows them to get up close to their favorite prey, little girls.
Double Subverted: Unicorns appear wonderful and glamorous due to their glamour, creatures unaffected by their glamour fear and despise them but hey, it turns out that the other creatures are actually seeing a second glamour and the true form of the unicorn is unknown.
Parodied: Unicorns are dopey and stupid in their adoration of virgins, and behave like overgrown lapdogs in their presence.
All Unicorns Are Different. Some of them really are pure, some not so, and some are plain daemonic. The Unicorn and the Virgin scenario may be very different depending on which kind of the Unicorn does the Virgin meet.
Unicorns are just another animal, nothing very special about them.
Alternately, they turn out to be the original medieval unicorns: Just because they're good doesn't mean they're friendly.
Enforced: "A beautiful magic forest, and not a single unicorn? Come on, there must be at least one!.. See, there it is!"
Lampshaded: "Didja ever notice how unicorns are surrounded by purity and goodness?"
Defied: The unicorn ignores the virgin in favor of the town whore.
Discussed: "If we're going to catch a unicorn, shouldn't we get a virgin? Come to think of it, does it matter if the virgin is male or female?"
Conversed: "Well, there goes that unicorn again, making the world a purer, more wondrous place."
Deconstructed: Unicorns friends of maidens turn violently against them upon the loss of their virginity. Unicorns lead raids to kill lumberjacks near their evergreen glades. Young girls have to be regularly given over to them in a manner resembling dragon sacrifices. On the whole, the effect is just like living next to any other sort of mythical monster because that's what it takes to get into fairy tales.
Reconstructed: But the unicorns are really trying to save the maidens from the brutal lumberjacks.
Played For Drama: The virgin that the Unicorn ignored in favor of the town whore is pissed off at being spurned. Unbeknownst to her, the unicorn is drawn to pure hearts rather than pure bodies and the town whore is one of those Hooker with a Heart of Gold types. And the virgin is plotting her revenge....