Use her

Natsu lay back in his seat, pulling his pants open and letting his dick pop out. Erza looked up at him, not wanting to act until ordered to do something.

Natsu simply grabbed her head, pulling it towards his dick. With a look of understanding, Erza's tongue began to slowly slither around his dick, guiding her lips down around it.

Her head slowly and methodically bobbed up and down along his dick - her professionalism seeming to bounce into this mental state as well - as she did her best to blow him efficiently and effectively.

He kind of wanted to see how she would react when given more express orders.

"Faster."

Erza continued, but it almost felt the same to him. The speed had picked up, sure, but it was just as proper. Just as perfect. Like doubling the time signature of a song. The music is the same, but faster. Erza was simply faster, but the pace was the same. Natsu was genuinely impressed. It was great to have sloppier sex with girls like Lucy, but he found Erza to be... more impressive.