John had always admired catpersons.
He was, to use a very old, very groanworthy pun, a cat person, himself. Not that way...well, a bit that way. John kept that to himself, though.
Sherlock was the most magnificent individual he'd ever met. That included his sleek black fur, and the sweet tips of his ears poking out of his curls, swivelling to catch new sounds. He couldn't help but envy the lash of tail as Sherlock grew excited about a case. They made John's hand itch to touch, but he never asked. Sherlock noticed, though. Of course he did.
An imperious headbutt against his hand no longer surprised John. It was instinct turned habit to gently stroke and scratch, revelling in the silky smoothness. It was also second nature to avoid the quick bite once Sherlock had decided he was satiated. He never deigned to use words for that, for some reason.
John had frozen the first time, completely unsure of what to do, before the irritated comment of "I have an itch, John," made him tentatively begin to move. Now he scratched deftly, eliciting rumbling purrs that he often remembered later in the privacy of his room. Sherlock had never made those kind of advances, after all, and John didn't want to ruin what they had. It was very good, what they had.
Then Sherlock twisted up to catch John's head in gently calloused hands, and John froze, not sure what to do. The moment they spent looking at each other was a small eternity. John tried to map sensation, intention, and the shifting green-blue of Sherlock's eyes, before it all blurred. Sherlock moved in, head tilted, lips quick against his.
"Oh," John said, a smile pulling his face into pleased lines, "well, then."
Clasped together, they tumbled onto the couch.