User blog comment:Omega natsu2/Chapter 385: Spirit King vs. Demon King, Predictions./@comment-77.194.131.143-20140523065533/@comment-7418318-20140523084755

@FTGM:

At least in the manga we saw Natsu use flames and lighting seperately once. First a flame strike that Hades blocked, followed one second later by a lighting strike from above that hit home.

Just because Natsu didn't use a pure lightning attack yet doesn't mean he can't. Natsu loves flames, they are literally part of his very identity, so maybe he just didn't want to or didn't think to use lightning by itself. We have yet to see him fight against an enemy who's immune or highly resistant to flames since he got the LFD-Mode. I'm not counting Atlas Flame in this context, since Natsu only ate his flames without throwing any attaks at him.