Disclaimer: I own nothing but the idea and the time put into writing it. Buffy and all characters therein belong to Joss Whedon and company.
They'd won. They'd thought they were done. That they could sit back and relax; train the mini-slayers - be consultants, only called in for the big apocalypses.
It was fine the first few years. They scattered, found slayers, trained them, and sent them back out.
But they forgot one thing ... they never thought to set limits on the activation spell, except the one to stop the activation of babies, children too young to understand. The Potentials, Slayers all now, from puberty to menopause. The spell didn't care if they were the Queen of High School, the President's daughter, insane, or killers likely to kill again. They didn't think and they were paying for it. The world was paying for it.
Slayer's started crawling out of the woodwork faster than they could pick them up ... not knowing to hide themselves ... some just not caring to. And with them, they brought the darkness - the demons and the vampires.
And the world knew.
And it feared.
Before long, you were just as likely to see a vampire feeding in the middle of the street as you were to see a slayer dust them and be shot down for it.
The world had turned against itself. After everything they'd done, every time they'd saved the world and it was them who'd ended it.
She was Dawn Summers and this was her story. The story of how she was going to save the world ... by stopping the end it before it begins. She was going to change history.