Mild slash and het warning. I don't own Harry Potter.
Remus is standing in a flat he hasn't been in in years, and the door is opening. Sirius Black stalks in, looking young and restless and exactly as Remus has always pictured him, exactly as Remus thinks of him when he thinks of him now. There is a moment of silence as Sirius drops his jacket over a chair and kicks his shoes off, his hair twisted and dripping from the rain outside. Then Sirius turns and looks at Remus, and his eyes have gone very dark and very smoldering. There are words to describe such a look, but it's one Remus has never gotten from Sirius before.
This is wrong, Remus thinks to himself, a second before Sirius winds himself up and pushes Remus back into a wall. At first he is gentle enough, but when Remus tries to get away his kisses become hungry and possessive. Remus feels like he is being consumed, devoured, and the next time he shoves at Sirius it doesn't quite work out right and he slices Sirius' arm to the bone. That's when he realizes that his fingers are cracking and shrinking, fur is sprouting through his skin, and a howling whirlwind has started behind his eyes. He bites down on Sirius' neck, feeling the shape of his mouth stretching even as he does so, and Sirius tenses for a moment before resistance gives way to limp muscles and slack eyes. Remus wants to howl in triumph or to cry out in horror, but before he can do anything the scene is gone, Sirius' pale face and long limbs crumbling away under his hands like stone.
Now the fur is shooting back into his skin, his claws lengthening into scarred human digits; the pain of the transformation is muted and pulsing. He sees Tonks, pink-haired and happy, coming towards him with a toddler on her hip. "!" she exclaims, leaning forwards to kiss him. The little boy watches him impassively from his mother's arms, brown-haired and golden eyed. His eyes are the wild cold eyes of a wolf, and something about his mouth is sharp and wrong. Remus backpedals rapidly and is caught by pale steady hands as dry and old as fall leaves.
Dumbledore regards him with a solemn twinkle in his blue eyes, and suddenly Remus is 11 again and in his parent's living room because that look is exactly the same as Dumbledore had then. He looks up into Dumbledore's wrinkled face, feeling again his insecurities and his fears, his loyalty and his awe, right down to the bare spots in the carpet and every little wrinkle in his clothes. "It will be hard, Remus," Dumbledore says, or said, and for the first time in years Remus believes him.