User blog comment:IamJakuhoRaikoben/Chapter 479: Who you should show the greatest respect to is, review./@comment-1938192-20160329142345

It could be like in Dragon Ball Z movie "Battle of Gods" where Goku could still fight at a level of a God even though the Super Saiyan God form ran out of time. Natsu's body probably still remembers how to fight with the Fire Dragon King Mode and it can replicate the results with it's own power. Cause it would suck if after a year of training the damn thing, everything you worked on just disappeared.