Jerk off.

You pull out and begin furiously beating your meat. The view of Winry's hips and pussy quivering in front of you drives you over the edge. You first blast of jizz hits and fills her ass crack, wuickly running off of her, dripping to the floor and running down her legs. One after another of your follow up blasts splatter her buttocks with your semen. By the time you are done her entire backside is wet with your seed. You swipe the head of your cock against her butt hole and she giggles and lurches forward at the sensation.

Winry turns her head and looks behind herself, still bent over her bed and on display for you. "Did you have a good time back there?", she asks with a smile. You most certainly did.