This is a variation of Challenge #1 at bloodshedverse pasted below. I don't know why no one took up this challenge. It sounds like fun. Taming a vampire! Just think. So many things to do!
So, I guess it should start when Spike shows up Buffy's first year in college And after Angel has left her. I didn't see what she was so angry about anyway. He was an ally. He helped her save the world. And she did let him walk away without a fight the last time he was in town.
So, Spike's return, right after the thing with Parker would get her thinking about his potential:
Angel (and her father) left her, giving her abandonment issues and Spike doesn't leave. He was with Dru for a hundred years. She saw him with Dru. He was good to her. Plus he keeps coming back to Sunnydale for some reason...
Her attempt to be with a human didn't turn out well. Parker only wanted a one-night stand, plus she was afraid of hurting him physically (and the sex was un-satisfying leaving her wondering about her own needs). She needs someone stronger, supernatural. They didn't make male slayers, so that leaves vampires. And suitable vampires don't grow on trees. Spike is a better match for her physically. And they'd had all this chemistry and inuendo between them.
She's not sure she believes in love anymore, so it's time to get practical. She plans to live, and she wants/needs a partner to help her do it.
For his part, Spike has that 'she's all around you' stuff Dru told him about to look into. Plus, there is an attraction. And he had fun fighting with her last time he was in town. Plus, he's perfectly willing to help stop appocalypses. And there are plenty where the slayer is. They shoulda asked him to help with the mayor.
Spike finds the Gem of Amarra which lets him go out in the sun, eliminating one of the draw backs of a vampire boyfriend.
Plus, maybe she had a prophetic dream or two about him. They were pretty inconsistent with the dreams. why would she have one about the gentlemen, but not one about the 3 demons trying to end the world in Doomed? Or Adam? Those seem more important than the Gentlemen in town to get 7 hearts. She should have had the dreams all the time.
So she wins the fight because she isn't so down about Parker, instead she's thinking positive thoughts about her new man, Spike. She gets the ring (while they are in the shade) and tells him something like 'behave and you might get it back.' She does not send it to Angel.
He still gets captured and chipped because the chip helps. She doesn't have to get him to stop hunting people. One less thing to nag about. But it's ok, he won't have it so long. It'll fail, get damaged, or removed somehow in less than a year.
He comes to them for help on Thanksgiving because she helped him get away from the initiative when they were attacked in the dorm.
And this is where the fun begins. She starts nagging him about changing his ways, helping her, becoming a better person etc. ( The nagging part is what I liked about the challenge. I think it is funny.)
Then the Will-be-done spell reveals what a cuddly, hand-holding, great kissing guy he is. Bonus.
She probably doesn't let on to the others that she's trying make him into her mate. She just says that they could use the help. Giles is on board, but instead of nagging, he manipulates Spike into situations where he has to help, or helping is just a side effect to him doing what he likes to do - fight and pose as the big bad.
So, as Spike goes thru his identity crisis as a vampire who can't hunt humans (not to mention the recent loss of Dru, his reason for un-living), all the same big bads come to town and the same apocalypses happen, just with more Spike. And a lot more smut. And Buffy nagging him every step of the way.
Obviously he would get positive reinforcement for good behavior in the form of sex.
Also suitable vampire mates are few and far between and a slayer is lucky when one comes along in her lifetime and shouldn't blow it. And when there are two slayers and only one Spike...
Theme:
So is this is Buffy being the slayer variation of a gold digger, trying to land the best mate for her rather than the richest? A scheming female? As opposed to Spike's love is everything attitude. No brains involved. While that sounds romantic, is it smart? He can afford to be foolish. He could live forever. The slayer needs to be smart.
It's like an arranged marriage, except they arrange it themselves. They always say that arranged marriages are among the most successful. While I think that is mostly because the women don't have a choice, I think it is also that the couple both accept that their spouse is their life and partner now. I think Americans place too much value on independence. And individuality.