Their rhythm is quicker now, but it's still careful, it needs to be and he can tell she's holding back just as much as he is. That would be almost frustrating in a way if this wasn't so good already. Once she's changed, everything will become new for both of them, all three of them, and Jasper isn't used to thinking of something as being transient, fleeting. This heat all around him, the fragile strength of her in his arms, it's all temporary, and he finds himself slowing again, savoring it as much as he can.

"Ne vsegda," he whispers, "ne dlja namnogo dol'she." It's rare that anyone like him is graced with this level of trust from a human, and especially when it's someone like Natasha, who trusts only when she's certain. He takes a slow breath, smoothing both hands down her back and up again, resting at her shoulders to keep her close as he moves faster again, rolling his hips, deliberately seeking out the little shifts that pull those soft moans from her.

It's a balancing act, it takes concentration, and at first he doesn't notice his own slow build of heat at the base of his spine, until she moves against him just right and her name escapes him in a whisper that sounds almost surprised. He leans back just enough to look up at her, open and unguarded and still dazed with all of this, but he wants to see her when she comes undone, he wants to know what that looks like and keep it.