They have a discussion.

"...so, Natsu..." Erza mused, looking up at him. "That wish you made was a good excuse to have some fun... But do we really need to stop there?"

Natsu blinked down at her, and processed her question, and before he could answer, Lucy threw in her two Jewels. "No, no you don't~!" she chirped. She then yelped as Lisanna elbowed her.

"Lucy, let them speak for themselves!" she chided, making the perverted genie pout.

"...you want to continue?" Natsu asked Erza, who nodded.

"Of course I do!" Erza nodded. "I've never particularly cared much for arbitrary sexual standards or nudity taboos. I only bother with following them to avoid getting arrested and whatnot. You know I've never been shy about sharing skinship with comrades. And honestly, now that you are using Lucy's powers, I'm interested in getting a piece of that action!"

"You go girl!" Lucy chimed again, this time, Lisanna stepping on her foot. "...should have had my tail for that one..." Lucy grumbled.

"...yeah, but what about Jellal?" Natsu asked Erza curiously, giving Lucy a look, and a gesture to be silent for the moment. She immediately complied, as her genie nature dictated when Natsu gave a command and meant it, and gave him a sheepish smile.

"We haven't really been able to pursue a steady relationship as of yet," Erza replied. "I hope that changes in the future, but for now, we're essentially free agents," Erza told him. "Besides, monogamy is bullshit, right? It's just a societal tradition, and arbitrary standard. Unless it's agreed upon within the confines of a relationship, I don't owe him exclusivity, nor does he owe it to me."

Natsu nodded, accepting her answer, before he finally stated, "Okay, so how do you want to approach this? As in, what kind of dynamic do you want, and do you have anything you'd like to use Lucy's sex magic for?"