User blog comment:Wrath022/Chapter 516: The Truth About Enchantment, Review/@comment-5303512-20161227040743/@comment-5303512-20161229044110

By that logic, Brain is still Brain since they are still the same person, just one persona is knowledgable and the other is destructive, that is just about it.

Just like how Natsu is selfless at times and fights for his friends, and the Etherious is killer instinctive to kill Zeref. Natsu have no killer instinct what so ever prior to Etherious essence awakening.