User blog comment:IamJakuhoRaikoben/Chapter 503: The Last Sight Seen, Review./@comment-84.197.239.101-20160926192137/@comment-5303512-20160927133423

Actually, Ice Devil Slayer powers is Curse, if you remember Bradman, he was able to use Ice Devil Rage too, he says that he doesn't use magic, but curses. And it would make sense that Gray would be the only one able to defeat END since he is the only one in the world with the powers to put him down.