Totomaru
I want Juvia and Gajeel to meet up with Totomaru and force him to join fairy tail. They all go on a mission where totomaru gets hit with a potion that ages him down 7 years. (Because Juvia jeopardized them and the bad guy only had that potion on him and saw totomaru first) so he is now their age
They get back to fairy tail and Juvia has started calling Totomaru “Toto-Sama”, then they start going on a lot of missions, so much that Juvia starts to ignore Gray and Totomaru playfully flirts with her so Gray will get jealous (he ships Gruvia and Gajevy).
One day Gray has enough and slaps Totomaru, Juvia gets pissed at gray and slaps him. Gajeel in a corner just laughing his ass off at the seen when a bolt of fire blasts him (curtesy of Natsu). It turns in to an all out war, Juvia, Gajeel and totomaru vs Gray, Natsu and (reluctantly) Lucy. In the end Juvia puts Erza in a water lock preventing her from stopping them and Juvia, Gajeel and Totomaru win the fight.
A few days later, Totomaru pushes Juvia into Gray, causing her to fall onto him and kiss him. She curses out totomaru and everyone is in shock at the water mage and Gajeel laughs so she curses at him too.
In the end the three friends change each other, Gajeel and Totomaru getting a little softer and Juvia wearing more black and turning a little punk, she starts being more confident and cocky (causing Gray to fall for her even more) and all of them are best friends