User blog comment:IamJakuhoRaikoben/Chapter 479: Who you should show the greatest respect to is, review./@comment-2214433-20160328191739/@comment-188.222.39.249-20160328233305

If we also remember when Natsu used Igneels power it was called blaze dragon king mode, blaze being a stronger form of a normal fire so this is probably just the base upgrade from his training