The first two times they had done this, she was in charge. She taught him what to do and he obeyed, even if he did take a few bold steps. But now, in this position, which the humans affectionately called doggy style, she was his. He started to move slowly at first, then he smiled a bit. His instincts were taking over. He leaned forward a little, his arms wrapping around her waist before he kissed her neck teasingly. "I'm glad it feels good for you...Because I like doing it like this." He started to thrust a bit harder than normal, his hips pressing against hers hard. "It feels right..." His ears were flat and he had a bit of a savage look on his face, his eyes looking more and more canine. He was losing himself now.
(How would you feel about her having sex with him when he is transformed at some point?)