The thing about sexual domination which Crowley has never entirely been able to get a handle on is all the effort it takes. Crowley is, despite his impressive creative streak and ability to be annoyingly persistent, fundamentally lazy. (This is not to say, of course, that there haven't been times when he's topped the-- Somewhere-- out of Aziraphale, but he suspects the circumstances in which most of those occurred would not be called healthy by any human practitioner of kink).

This, however, makes rather a nice compromise. He breaks the kiss with a wicked little bite, leaning back to watch Aziraphale's face(with what he'll insist is smug enjoyment and nothing more) as he shoves his pants aside to get his prick out. All he has to do is recline and squeeze, slow, rhythmic undulations while Aziraphale writhes above him. And Crowley gets the hard warmth of the angel's cock in his hand as he lazily toys with it, and surround sound of his moans as they bounce off the water. Gorgeous.

His own skin is growing flush with arousal; he can feel it fizzing all down the length of his tail like the remembered itch before moulting, the consuming, distracting need to slough off his old skin. It's not at that point yet; a pleasurable anticipation rather than desperation, but it'll get there eventually.

'Sooner or later,' he breathes after some moments, 'you're gonna have to tell me exactly, how, er, ssssnakey you want me to be.' He's always had less control of his physical form when he gets-- worked up; he doesn't want to ruin the mood by accidentally manifesting the wrong kind of genitalia.