As well as one could expect from Lucy

As Lucy continued to fuck Natsu with her tits, Erza crawled over and joined her - their breasts pressed up against one another as they both rocked up and down - a glare forming between them, never breaking eye contact with one another.

Natsu could practically feel the energy boiling from them as they stared each other down in a rage.

"So Master, whose are softer? Obviously mine right? Because I'M the real Lucy" Lucy huffed

"Oh please. Obviously mine are softer." Erza huffed.

To be fair, Lucy's WERE softer - mostly because Lucy lacked the musculature Erza had, but for the sake of this contest... He wanted to play it up.

"I dunno. Feels the same to me" he shrugged

"What?! Her tits feel like boulders!" Lucy proclaimed.

"Excuse you?! Yours feel like bags of wet cement!" Erza hissed.

The two women both snarled, beginning to move their tits with more speed and fervor than before. Honestly, Natsu was more focused on this little rivalry than the actual sex part. For now, at least.