Natsu backing down worked for me. Even though Gildartz has always fought him in Natsu's childhood, he's always either been going easy on him and/or been in training mode. Natsu has never been blasted with sheer raw power before, and all he shut down upon the realisation that there is no hope in hell that he can beat Gildartz as he is right now. The Phantom Lord would have been the only other person I'd say who could be stronger than Gildartz, but Makrov took care of him. Perhaps Ultear as well.
Yeah. I dig the OP, and even more so since it contains Mira fairly prominently this time round.Mirajane's sole presence scared the crap of Elfman and Evergreen. Awesome.