Nice and slow.

You slide the tip of the strapon up and down Emily's wet slit a few times before guiding it inside, studying her face all the while. Her eyes are closed and her lips parted, her cheeks flushed. When you move forward to push the dildo into her she draws a deep, shuddering breath, arching her back to thrust her pert breasts up. You slide your hand up her body to cover one of them, feeling her heart beat as you squeeze it gently.

When you pull back a little Emily makes a soft, frustrated noise which makes you smile. Already so eager!

You reward her by pushing in deeper than before, starting to fuck her with a slow, steady rhythm. The look of intense concentration on her face is adorable, and you love the way she strains against her bonds to meet your thrusts. Her soft whines of frustration when you pause for just a moment makes your own pussy wet - teasing a young, eager girl is one of your favorite things, and the fact that this one is your own niece only adds to that pleasure.

You continue with your slow pace for a while, supporting yourself with one hand while you play with her breasts with the other, occasionally letting her suck on your fingers which she does eagerly.

When you start to increase your pace Emily strains more against her bonds, clearly frustrated in the most delightful way.