Basically, what if Buffy and Spike were reincarnations of various Slayers and vampires who fell in love over the centuries? 

Buffy and Spike begin to share dreams about their past selves. They're in denial at first, but the various memories and shared experiences cause them to fall in love. 

There's major freak out among the Scoobies, which leads to rapid research, lots of wigging and Buffy feeling insecure for disappointing her friends, which should eventually lead to recollection and understanding. Even from Xander. 

Is there some sort of conspiracy going on with the Watchers Council? They must be aware since it's happened a lot. 

Angel finds out about what's going on and misguidedly believes he's the reincarnation of the vampire lover, and can't understand why everyone thinks it's Spike. 

How long has the reincarnation loop been happening for? How long will it last? Can Buffy and Spike break the loop? 

Can have a claim.