I find it hilarious how Gray is so obsessed with it right now, considering the whole guild is otherwise fighting for it's very survival and Natsu (END from Gray's pov) is still only looking for Zeref. I guess Gray reckons that he will first defeat Natsu and then single-handedly defeat the rest of the invaders, Zeref included, despite the fact the was just before having such a super hard time against an underling.

The dude really has his priorities set correctly. He must have frozen his own brain.