There’s a kid in many of Willow’s class that’s a bit too curious of Sunnydale’s mysteries for his own good. Why does she keep seeing him around? James, on the other hand, was hoping fervently that he didn’t have to see Buffy mooning after Angel or vice versa, and couldn’t stop wishing that Spike would be here soon. Never mind that William the Bloody was still his destructive, unsouled self just then.
 
Before that he had things to do and futures to influence. Sooner or later their fears were going to manifest in the physical world, the butterfly effect has made things worse, and the Scoobies will have more than they can handle. James might even get what he wished for as Spike and Drusilla barrelled into Sunnydale at a moment unexpected. Beyond all that the apocalypse is still coming. 
 
An unsouled master vampire who had killed two slayers and the vampire slayer. They don't really have much in common with each other, right? There's also only a snowball's chance in hell of anything happening between them? Well, James begged to differ, and he would do his damnedest to make sure the conditions were favourable for them and stack the odds in their favour.
 
(The vampire!Buffy tag for story is basically for the Season 1 episode, Nightmare. Technically, it's not permanent.)
(Another warning for 'blood as a food group'. This story didn't shy from the details of that when we get to the vampiric bits).

Part Two of the Something Wicked series  (S5, beginning with "Buffy vs Dracula")

Spuffy have been together for a while now.  Things have been great.  The Scoobies have more or less accepted the reality of their couplehood, Spike finally has his own place, so there’s plenty of thoroughly excellent shag-time, and college is kind of fun when you have a worldly, undead tutor to poke fun at your instructors and help you remember your lessons with fascinating anecdotes or, when that fails, incredibly memorable sexy-times.  Life is actually, like, bordering on good. 

But then Mr. Eurovamp 2000 blows into town and causes a bunch of jealousy.  And then Buffy starts having a bunch of crappy Slayer dreams about glowy purply stuff.  And Dawn is going off the hook even more than usual, and Mom is acting weird…  And, as if there’s not enough to deal with, Buffy’s pretty sure that idiot Riley Finn is still lurking around town trying to come up with a reason to shoot her boyfriend…

Buffy should have known things couldn’t stay yummy for long.  She probably would have started to worry if it had.