User blog comment:IamJakuhoRaikoben/Chapter 411: Quid Pro Quo, Review./@comment-24536822-20141202022006/@comment-85.75.17.61-20141202222215

Probably Natsu's magic has developed so much that he doesn't need an external source of energy to achieve DF, but he can do it himself. I think it was due to all the fighting he was extremely tired in order to use DF for a prolonged fight. Sting's and Rogue's tank of magic isn't big enough IMO so that's why their DF was not that powerful. Maybe the lachrimas gave them the powe to achieve it, but it is not as strong as Natsu's yet. By the way,what rank do you guys think Natsu is now in terms of power. Seems to me that he ( and maybe Gray ) has surpassed Erza and we all know that with DF he has overpowered Jellal, so he potentially is at Laxus'es lvl or a bit below the way i see it.