HAIR
Harry and Ginny had always had a simple – and kind of weird – obsession in common. And it's a fact that Ginny unconsciously knew about Harry's obsession, and Harry unconsciously knew about Ginny's obsession, but it was like they didn't, because they never talked about it.
The object of the obsession was the hair.
Harry found it fascinating how Ginny's hair was simply perfect. The color glowed in a tone he knew was unique, even between the Weasleys, no hair was like Ginny's. The smell, of course, had been the first thing he noticed in her and he never stopped noticing it, that floral scent that even after so long still got him intoxicated. And the softness was so good in his fingers, when he stroked her locks or when he held it to put her mouth close to his.
And Ginny did also love Harry's hair. The main reason was that it was unique. Of course, there were a lot of people with messy hair. But not like Harry's. His hair was messy – of absolute stubbornness, marrying perfectly with its owner – but was… pretty. It fell everywhere disobedient, but was straight and really soft. It was just… rebel (like the owner). And Ginny loved. Ginny loved to lock her fingers in it when they kissed, loved how it got a little longer and hindered Harry's vision when was wet, loved the darkness of it that contrasted so much with his skin color and eyes.
They just loved each other's hair, and it was one of the many things in common that made them so them.