The White Mage had infiltrated the guild and used her spell, whiteout, to brainwash everyone into being her followers. One of which was Juvia. The White Mage had sent her out on a mission to bring Natsu, Erza, Wendy, Lucy, and Gray back to the guild so she could brainwash them too

Natsu and the others were already on a quest and were on a train to get to their destination when they were met with a big surprise

Juvia: Gray-Sama, your faithful Juvia is here. She smiles

Everyone was surprised to see Juvia show up out of the blue

Gray: Juvia?! What the hell are you doing here?! He says in surprise

Juvia: Hm? Why, Juvia came to see you, Gray-Sama. She says, still smiling

Gray was still a bit in shock and felt as if something was off

Juvia: Sama? She asks, tilting her head and smiling

Charla: Well, since you're here. Why don't you join our quest?

Happy: Yeah! Join our quest!

Juvia sits down next to Gray

Lucy: So, how is everyone back at the guild?

When asked, Juvia pauses for a moment as if something was conflicting inside her

Erza: Are you alright?

Juvia: Hm? Oh yes, Juvia is fine. Everyone at the guild is doing great. She smiles