When Zack had first caught Umbreon, she didn't really have that much of an anal fetish, as she teased him there to mess with him before Since then, she had gotten more active with it, and she was usually the one stirring up his anus with her skilled tongue. And while she was used to giving the attention, she clearly loved how Zack tried to outdo her. She yelped a couple times as he smacked her rear, making her firm rear jiggle a little.
When he had prepared her enough, Umbreon gave her hips a teasing wiggle, wanting him to take her already. She watched as he positioned himself at her entrance, slowly pushing in. He'd find that her anus had a bit more resistance than Espeon, and he just might find himself breathless if he wasn't prepared.