User blog comment:IamJakuhoRaikoben/Chapter 398: The Final Duels, Review./@comment-25111584-20140903065859/@comment-7418318-20140903091727

Natsu could lose Happy, which would make a lot of people very happy, though not me I guess. I'm rather indifferent to the matter.

Or Zeref might get interested in Lucy because she summoned the Spirit King and abduct her, making Natsu temporarily lose her.

For Erza there's only really two: Jellal and strawberry cake. Maybe her favourite cake-shop was trashed by Plutogrim. That'd put her in a murdering mood for sure.