Obviously, this is AU. I will be changing Buffy's past quite a bit, much of which will be explained as the story goes on. The only obvious plot hole there will be is that even though Buffy died twice, there is no other Slayer. I will try to find a way to explain that later on.
Summary: What makes someone be a potential Slayer? A small accident allows one Slayer to pass by unnoticed, until her past comes to catch up with her.
Pairing: It's inklings of Ron/Hermione, but nothing large so far. The main pairing is most likely going to be Buffy/someone else. I'm not sure, though. Not Spike or Angel. If you have problems with my pairing, don't yell at me about it, write your own fic.
Timeline: I know that the timeline is wrong. I know it. Don't tell me how it's wrong, it just didn't work correctly if I actually did it right. This takes place when Buffy is 25 and Harry is fifteen.
Although many don't realize it, the Slayer is a creature of magic. Her body, the vessel in which her strength and other supernatural abilities are carried, cannot be a normal human body. A normal body would be overwhelmed by the power imbued in it, but one too magical would not suffice either. The different magical energies in the body would conflict with each other and cause great pain. A potential must have enough magic in her blood to handle the power they might be given, but not so much that it would disrupt the balances in her body and potentially destroy it.
The Watcher's Council, which had been researching and battling the dark forces of the earth for generations, stumbled upon the slayer by a turn of fate. After this discovery they realized that, with a bit of magic, they could find those girls who had the ability to become a slayer and train them from the beginning. This task was long and difficult and could be performed very rarely. As such, they had a very hard time locating all of the potentials and were lucky if they could find one slayer in every generation or so. Those potentials they did find were stolen away from their homes and hidden while they were trained for the time they might be called as Slayers.
In another twist of fate, the Watcher's council became aware of a group of people possessing magical powers. They had created a whole world right under the noses of the non-magical people. Realizing that they could have a potential ally in their fight against darkness, the Watcher's Council approached the magical government and explained to them who and what they were. This was a stroke of luck for the Council, because it became clear, after only hours of speculation, that all the potentials were the direct first-degree descendents, or daughters, of wizards, but not wizards themselves. The more common term was 'squibs.'
The magical were wary about working with the non-magical, though, and it was decided that the two groups would be aware of each other, but not work directly together. There was an established agreement made between the two parties that could never be changed or broken without severe penalties for the offending group. The Council wanted complete autonomy and stated that no one in the wizarding world know more than what a slayer is, and what she does. They also wanted a list of all the female squibs born and permission to take them from their homes for training in order to ensure the greatest chance of success. The governments of the wizards, wanting to have as little association with a muggle organization as possible and believing that the slayer, not being witch, was not their responsibility to deal with, agreed on the condition that they would be informed of the identity of the current slayer and have the ability to call upon her whenever a slayer was greatly needed.
The agreement made and adhered to, lasted for centuries, over a thousand years, to be more specific. The Council was provided with the potential slayers to train, while their partners received the ability to call on a trained soldier in dire need without expending the time and resources to train all the girls that had a small chance of becoming that soldier. Both groups were happy with the arrangement and continued to be on good terms for the majority of their association. That was, until new slayer was called.
This time, though, none of the potentials were called. The Council accused the wizarding world of treachery, the wizards believed the Council to be hiding the true Slayer, not wanting to share her. After careful review and full disclosure of all records, it was proven that neither had deceived the other. The magic that the council used to locate Slayers in the past was old and lost to them, and the Slayer could not be found.
Two theories emerged in the world as to what happened. The first theory, and the more popular, was that due to the recent significant decrease in demon activity there was no Slayer anymore. Many couldn't believe that their careful methods had somehow missed a girl. The other theory was that there was a Slayer out there, unknown and hidden. In case another Slayer was called, the council continued to train potentials until they reached eighteen, which is the oldest a Slayer can be when they're called. And so, the two groups passed ten years without a Slayer.
Sunnydale, CA.
A persistent tapping awoke a young woman from her sleep. Annoyed, Buffy groaned as she sat up, rubbing the sleep away from her eyes. When would people learn that seven o'clock was not a good time to come calling upon a tired Slayer? Briefly, she considered going back to sleep, but as the tapping became more insistent, she realized that it could be somebody who was in trouble. It was just as likely that it was a demon wanted to be hurt really really badly. She hoped it was the latter.
"All right, all right, I'm up." Buffy groaned as she put her feet on the floor. Sometime between standing up and reaching the door, she realized that the noise was not coming from downstairs. Frozen, Buffy stopped and listened to the sound, praying that it wasn't coming from her window. Please, please, let it not be what I think it is. The Slayer turned around and stopped breathing. An expression of utter terror was on her face, something her enemies had never seen. In front of her, tapping on her window, was an owl. No. Please no.