He doesn't need to

"You won't get away with this!" She said. "Juvia will get him back! You won't stand in the way of our love!"

"Never wanted to." He responded.

"Let Juvia go!" Said Juvia. "Juvia I'll return and..."

"Oh, really?" He interrupted. "I don't think that's what you want"

"O-of course that's what Juvia wants! W-w-what do you mean?"

"Well, for starters, it's not like I couldn't hear you moan earlier. Don't think I can't smell how wet you are, and I'm not talking about the fact that you're made of water. Speaking of which, you could just turn into water right now, there is no way I could hold you if you did that. In fact you could probably even filter through the ground, and then I would have no way to prevent your escape".

Juvia averter her gaze. "Juvia d-didn't think of that."

"Of course you did. You just don't want to. You know what I think? I think you are letting me restrain you. I think you enjoyed what you saw, and deep down, you want to see more." Responded Natsu. Juvia didn't want to admit it, but she couldn't find the words to deny it either.

"Don't try to hide it. You loved seeing me having sex with your crush. You want me to continue. You want to see how he fucks my face. You want to see his face of pleasure as I plow his ass." He continued, while he crouched, getting his face close to hers. "And you wanna join in on the action."

Hearing that, Juvia locked eyes with him again. "No, Juvia..." She started saying, but the words never came.

"Oh, come on, I can see how the thought of having sex with two hot dudes turns you on!" He said, while using his free hand to squeeze her boob. Juvia squirmed, moving her legs and rubbing one thigh against another. Seeing that, Natsu gave her a kiss. Despite her verbal and mental struggle, her body reciprocated. Even after that, she still looked defiant.

"That's not... Juvia likes him, not you." She said.

"Doesn't mean I'm not hot." He responded, after which he let go of her wrists. "You can lie to yourself if you like. Return to the guild, overthink how to win him, whatever you want. But my offer stands. If you decide to be honest with yourself, you just have to follow me." After that, he turned around and started heading back to the clearing.

Juvia stood up. "Then Juvia will return to the guild." She said as she started walking in the opposite direction, but her body wouldn't move more than two steps. Reluctantly, she turned around and started following Natsu, accelerating her pace to catch up to him. "Why is Juvia doing this?" She thought.