Responses

I had this same worry after the year skip where Gray was infiltrating the evil organization, before we knew he was undercover. I was worried Hiro was trying to make a Naruto/Sasuke rivalry, but was happy when he trolled us and it was just a cover. So hopefully we'll get the same here. Especially since Fairy Tail is all about 'family', and Gray will be like Happy and wont do anything. At least until they defeat Zeref, and then Natsu will probably force Gray or Lucy to destroy E.N.D.
I really hope that Hiro doesn't turn Fairy Tail into a story like Naruto, with the having Gray and Natsu fight just because of reasons. I really hope Hiro is trolling us with this, and the next chapter Natsu and Gray just smile at each other, and take off to go fight Zeref.