Genesis has started noticing when Sephiroth is anxious, or trying to mask something. In this case, that laugh, followed by Whatever it's too suspicious to ignore. Obviously he has thought about this, more than once in private and at night. He always thought Sephiroth would prefer an active role, and to make him submit would require a fight, to overpower him.

This is... different. Genesis doesn't know what to do with that much liberty, so he moves closer and kisses his jaw so that he can whisper to his ear.

"Isn't there anything you would like to try? Do you want to be in control, or to give control to me?"