Itachi imagines it would go something like this:

Grinning manically, but too bent on what he's about to do to care, Itachi catches Sasuke's flailing legs and throws them over his shoulder. His brother's hole is now twitching and bared before him. Sasuke's eyes are wide; he's not used to seeing his Aniki like this, so out of control, so deranged.

Itachi's own eyes reflect red back at him and Sasuke shudders.

"Ready, Sasuke?"

Sasuke blinks, surprised. Itachi never says his name, at least, not like that. Not so full of…of something Sasuke can't identify.

Itachi takes his blink as his consent and in one swift thrust forces himself inside his baby brother.

Sasuke screams and Itachi feels as though he's just been given the world. Not to his surprise, he finds he wants more. And so he takes and takes. He keeps on taking until Sasuke's wails fall silent as he climaxes. As Itachi slowly descends, he finds that Sasuke has passed out.

Because this is a dream and Itachi can do as he likes, not that reality stops him anyway, he bends down and softly kisses an unconscious Sasuke. He remains within Sasuke, wanting to be as close as possible to his brother. He can do this because he knows it's all either of them ever wanted.

~Fin