User blog comment:IamJakuhoRaikoben/Chapter 499: Gray and Juvia, Review./@comment-26389992-20160829153411/@comment-30807545-20160829164841

Better yet, Larcade could be a biological clone that Zeref concocted using remnants of Natsu's DNA and a piece of his own, which would explain his appearance. His personality and powers could be to serve as an antipode to Acnologia's, which would explain why Zeref would see him as a "secret weapon" to use against the black dragon.