i think you need a shotgun blast
"She is not the Slayer and he is not the Slayer’s Watcher, but their roles are almost as old as human civilisation and they fall into them without even truly having to try. She kills twenty or thirty vamps a night, and he stands at her shoulder, twisting cheesewire between his fingers that he’s cursed with a spell five centuries old, a stake in his belt and blood between his teeth"
Joan Watson is a Slayer, and Sherlock Holmes is her Watcher.
This is how AU's are done! Beautiful, achingliy beautiful. It hurt me. I love it.