Swellingly!

Emma and her penis find their target and start to stretch you open. Her eyes are wide; she didn’t expect to be making progress right away! You are amazed that you feel no pain as her head stretches your rectum without full penetration. She feels it too and keeps pushing, as if to say this massive cockhead is going to fit in there without going into your colon. You gyrate to help her stretch you in every direction. That massive cockhead, which has your ass parted completely, keeps disappearing into your anus but going no further. The bulbous bulge in your abdomen coincides with her flaring head popping inside.

Emma grins widely in triumph. Then the corner of her mouth twitches as she cums. This *does* go all the way inside you past the barrier that her cock has been straining against. Your middle swells in front of her eyes, which express pure glee!