It's all about the right formula...
Dark haired, sometimes waif-like, brainy, smart ass + light brown or blonde haired, brave, stronger, not as intelligent=chemistry that seems to work for slashy fandoms everywhere! Not all descriptors fit all pairings mind you. Because YES. I am AWARE that Vulcans are stronger than humans, for example. Just go with it though, m’kay?!?!?
Edit: These too!!
And Drarry, though in reverse: