In this case I'm talking about an actual girl. Probably someone 6-12 year's old would be an ideal audience (although with some changes it could play well for someone of any age). Why would you want to win the heart of a 6-12 year old? Look, creep, what do you think I'm getting at? I'm saying this would be a great trick if you have a daughter, or a step-daughter, or a grand-daughter, or a niece, or a young family friend. Maybe you're dating someone who has a daughter from a previous relationship. Perform this for her kid and win both their hearts. If you, for a second, thought, "Hmmm, I hope this is a good trick to seduce a 6-12 year old girl." Please, go find a falling piano and stand under it.
It could also be performed for the birthday girl at a birthday party, or a kid at a particularly important table in a walk-around setting. I say "particularly important" because there is a bit of an investment each time you perform it ($5-$10) so it's not something you would do for every table with a young girl. I've only performed this once for the daughter of a friend of mine, but I will be doing it again the next time I see my niece.
I will kind of walk you through the effect, method and presentation all at once.
You tell the girl, "Hey, I bought you a necklace," and you bring out an empty chain.
Now, because most little girls are naturally sweet, she may be -- or at least act -- genuinely happy for this piece of nothing. However, if she's like, "This sucks, what a dumb gift," then I hope that's not your daughter or you're in for a life of misery. If it's the daughter of someone you're dating, then she learned that behavior somewhere, and it's probably from mommy. So your best bet is to say, "Deuces, bitch!" and run away and don't look back.
Okay, so let's go back to the point that you pull out the chain. After a couple moments you should look at it and say something like, "Hmmm... this is kind of a boring necklace. I think you need something with a little more flare. I have an idea." You take the necklace back and at some point in the ensuing action (which can take anywhere from a minute or so to 10 to 15 minutes) you're going to switch it in your pocket for an identical chain with an origami crane pendant on it.
You pull that necklace so it hangs out of your pocket with the crane itself still in the pocket. In other words, you take the bare necklace chain back, put it in your pocket, and then pull out the chain for the necklace that has the pendant attached. You will probably want to have a wallet or something in that pocket to keep the two necklaces separate.
Now you have a few options. You need a small paper crane folded from flash paper. Here are the three options:
The Pragmatic Option
Just have one already pre-folded in your wallet and take it out. Let the girl examine it.
The Magic Option
You're going to magically produce a folded crane. There are a bunch of different ways you could do this. The simplest is probably to have the crane "palmed" in your left hand, and a thumbtip on your right thumb. You bring out a piece of tissue paper in your right hand stroke it between your hands, dropping of the thumbtip into your left hand. Then poke the tissue paper into the thumbtip and steal it out of your left hand. When you open your left hand up, the paper has "magically" folded itself into a crane.
The Arts and Crafts Option
This would only work in a casual situation, but I think it's the best option. Instead of producing the crane in some way, sit with her and teach her to fold one. She folds one with a piece of origami paper, and you fold one with a piece of "tissue" paper (in actuality, it's flash paper).
Either way, when you're done you tell her about the symbolism of the paper crane which is a long life, happiness, and good luck.
You remove the chain with the crane pendant from your pocket, hiding the pendant in your left hand which is holding the chain from the top and allowing the rest to dangle freely (Dangle Freely is my porn name.). You take your flash paper crane and wind the tail around the chain (alternatively you can just crush the crane around the chain, or you could try and attach the back of the crane to the chain so it more resembles what it will look like after the transformation, if that matters to you). Light the paper and in the flash of fire, drop the pendant from your left hand, it will appear where the paper crane was moments before.
Give the necklace to the girl.
You can find these necklaces cheap online for about 5 to 7 dollars each. Buy a few. Some people try and sell the same ones you can get for cheap for like $25 bucks. Avoid those people.
You can, of course, find nicer versions of these necklaces, and you could do this as part of a real gift for a woman of any age. I only recommend it for a young girl because 1) you can do it with a less expensive necklace and not feel cheap and 2) a young girl will be happy with pretty much any necklace -- 8 year olds don't have a well established sense of style. Just because you can give this gift as part of a trick, doesn't make it a good gift for just any woman. Does she like origami, birds, or Japanese culture? Okay, then it might make sense as a gift. Otherwise, get her something she'd actually like and quit shoving your magic where it doesn't belong.