Urgh, yeah, okay, I think you're right about that. "Seemingly unrequited pining" is the specific (sub)trope in which both characters like each other, but manage to have misunderstandings, or both think "I like them, but they're so great that they couldn't possibly like me back!" or whatever other devices we use to keep two characters pining for each other even though they both actually have the same feelings. ;-)

Whereas UST in general... first I was mad that it's not on this list, but then again I don't even know if it could count as a trope – sometimes it seems more like UST is the Bedrock of (Almost) All Fanfic Ever. (And I don't mean that at all as a bad thing!)

So, fiiiine, I take it back, Seemingly Unrequited Pining, while fun, is nowhere near my single top thing. Back to Found Families it is, then. :D