Hi -- sorry for the late post -- just found your LJ. Although I write it, in general, I'm not a big fan of rival/slash (lol) for the reasons you mention. Mainly because there's such a temptation to make said rivals cuddly, whic usually disregards not only their history, but their very characters. I mean if you look at Kaiba's relationship with the only person (fanfic spec aside) he loves -- Mokuba -- although he'll literally die for him in a heatbeat -- he needs to be facing death to give even a hint to Mokuba how he feels, has never told him he loves him, and hugs him exactly once in the manga -- after they are reunited at Duelist's Kingdom. This is not the kind of guy who's going to be singing and bringing flowers because he's gotten laid. And Yami (yeah I was getting to him) isn't exactly Mr. Warm and Fuzzy himself.

That said, I think the reason I see them working is because so much of their rivalry is about, as Yami says at Alcatraz, their bringing out the best in each other -- as people. There is a real sense that neither will settle for the other being less than they can be -- and that goes beyond the dueling field. Like if Yami teaches Kaiba something about accepting his past (and by extension himself) at Alcatraz, and about the futility of trying to use anger to sdestroy his hatred -- Kaiba in his duel with Isis teaches Yami, who is so focused on his past -- that everyone has a responsibility to create their own future. It is this sense that their rivaly is really an expression of their caring, that for me can turn rival/slash into a OTP.