This is actually one of the more sad couples for one thing: the race of Ice Apparitions (or, in Jap., the Kôrime. Thanks, Armand!!) are all females and despise males...Yukina's an Ice Apparition...and Kuwabara's a guy.
But what's cute about this about this is that even though Yukina doesn't seem to return the affections, Kuwabara obviously loves her with all his heart and soul. It's really sweet how he goes on about "I'll fight for you!", and who can forget the "Kuwabara *heart* Yukina" headband!! >D It's just so cool, I have to worship in my own shrine.
Problems with this relationship, you ask? Well, other than the ones mentioned above....HIEI. Hiei, as we all know, is Yukina's twin and is (in my mind) a little overprotective. And he doesn't exactly think much of Kuwabara. So, of course, he's going to supremely pissed if these two EVER get together like they should. Keep your fingers crossed!!!