User blog comment:FairyRaven/Fairy Tail Chapter 363: The Stories That Demons Read, Review and Commentary/@comment-1153699-20131207173113/@comment-1359322-20131212101037

Who knows maybe Dragon Slayers were meant to have multiple elements from the start, since 400 years ago, there were many Dragons still alive, maybe a single Dragon Slayer was trained by several Dragons so that they could fight against the enemy Dragons more effectively.