HE DIPPED HER, YOU GUYS! HE FREAKING DIPPED HER! Why do I need to explain more than that?
Okay, so I know the pictures I used are from a time when they’d lost all their memories, but I actually think that episode’s still worth considering. Willow and Xander wake up snuggled together with her wearing his jacket and their first guess is that she’s dating Xander’s brother. Giles simply resting his head on Anya’s shoulder is enough to convince them they’re together, and the engagement ring is taken immediately as proof. Willow and Xander don’t connect as a couple during the spell, and Willow is still attracted to Tara. Buffy and Dawn come together naturally as sisters, but Giles and Spike as father and son are just as awkward together as Willow/Xander. The only fake relationship in the episode that clicks is Giles/Anya. They bicker, of course, but when they make up there’s real affection and passion there.
Tabula Rasa is fun and super-shippy, but my favorite episode for the two of them is Grave. Throughout the series, we see them connect in ways they don’t with the others. Whatever they might say to one another, they treat each other like equals. And really, that makes sense. They’re business partners. They’re both older than the rest of the group and they both have dark pasts. They’ve seen so much more and have so much more experience with the world than the others, so it’s not really much of a surprise that they can have a friendship with one another that exists outside their relationships with Buffy and Xander. Grave, though, is really the best example of how much they really mean to one another. The beginning, when she vies for his attention by mentioning her new hair color, is very childish and sweet but the episode moves into much heavier territory when Giles is injured and Anya is keeping him company while he presumably dies. Watching her cry over him and beg him not to die because she’s got so much left to tell him is heart-wrenching. When he lives, Anya puts her arm around him and helps him leave their demolished shop.
Anya/Giles would be incredibly funny and even a little bit sexy, but most of all it would be that last moment between them in Grave - two people, walking side-by-side through the ruins, holding each other up. But probably with a little more bickering. And some slap-fights.