He's not sure what to think of their game - not even sure this is a game at all. And really, he concedes, if it is anyone's game, it is hers. After all, she's the only one who actually knows the rules.
At first, she lingers in the shadows of his newest location like a query that wants to form but remains nebulous at the back of his mind. He acts indifferent, but he remains hyper aware of her position all the same. It isn't some great talent or honed skill - no matter how she conceals herself, her presence seeps into him and will not be removed, as it has from their first meeting.
Her reticence does not last overlong. He never expected it would. Natasha may clothe herself in darkness and secrets, but she cannot ever be accused of being shy.
She begins sharing the same space and trading one-liners with him in short spurts.
The first time he risks bringing out the other guy since Thor's adoptive brother brought something like Hell to Earth, he does it to save a bus from falling into the Thames. She stays within the periphery and tosses him new clothes after he reverts back. After thanking her, he pulls on the necessary articles and then calls over his shoulder as he leaves, "Wales."
When he helps protect against a local terrorist group in Camlann, she has the big guy's back. It's when the dust settles and the smoke is still clearing, but everyone else is long gone, that he stands before her and she holds his things to her chest teasingly that he backs her into a tree. She somehow manages to find leverage and before he has even diminished to his natural form, her mouth is on his own, her hands gripping rapidly shrinking shoulders as his change of clothes falls to the ground, forgotten. Pulling back, she grins at him and declares, "I win."
He lets her think that - after all, he rather likes this game.