Hi EddyxMarvoloxRiddle,
Ufortunately, this subject never got the importance it deserved on the show. And don't get me started with the double standards between Angel's curse and Spike's quest... Well anyway, here's one story I think might fit your request:
Fangs, Wings, and Other Things by Soulburnt
Summary: After failing to stop Buffy from turning herself into the police for a murder she didn't commit, Spike picks himself up from the alley floor and heads to Africa to get his soul. When he steps out of the cave, he's met by a delegation from the Vatican. They're not there because of his soul (which is perfectly nice and all). They're there to be a support team for his demon. Spike finds he is suddenly emitting the most wonderful scent of roses, is preceded everywhere he goes by the sweet chime of bells, and that he occasionally sprouts wings. None of that matters, though – he needs to get back to Sunnydale, preferably before Tuesday rolls around.