1. Spike having to protect Xander
2. Spike realising Xander's worth/potential when he's overlooked by his friends
3. Spike having to woo Xander (who may or may not be oblivious)
4. Spike claiming Xander or taking Xander as his pet
5. Or any combination of the above
I've already read/am reading orchidluv 's 'Nothing the Same' as well as yanagi_wa 's 'Ulterior Motives' and stillrose 's 'There's Always a Sneer in Vegas'.
Please don't rec anything archived on spanderfiles because I'm already making my way through those fic!