
the book of END is something you can't open or damage unless with a very strong magic since it was sealed by zeref himself. So i think they would attack it with a very strong magic with the intention of destroying it, but end up unleashing END, who is actually Natsu. I wonder how far do Mavis and Makarov know..do they know about Natsu?

I love how the author hinted on this event when he wrote the filler in the anime where Gray surrendered Natsu to that dragon-obsessed girl, not knowing that she wants Natsu to power that a Dragon machine.
Grey is so set on getting E.N.D. i wonder what he will do when he finds out who E.N.D really is >-<