Dang. That was something for the 400th chapter... that explains why they got blocked by Freed's runes... although, if Igneel was really inside Natsu (same with Gajeel and Wendy's dragons)... why didn't they come out during the Tenrou? Hmm. I guess it has probably something to do with Mavis saving the guild... and hopefully we get an explanation behind this.
The dragons being inside dragon slayers kind of make sense too, if we think that the real power source of magic of dragon slayers are the dragons inside them!
Can't believe we will see the goal of Natsu, Igneel was with him all along. Damn... since Igneel appeared, it feels like this is going to be the last arc or so of FT.