User blog comment:Wrath022/Chapter 516: The Truth About Enchantment, Review/@comment-5303512-20161227040743/@comment-1359322-20161228142651

Brain and Natsu are different individuals, you can't just compare them as if they're the same person. Besides if you actually want to use that as a comparison i can use Laxus in the Battle of FT arc as an actual example too.

Laxus became aggressive near the end of it and almost killed Natsu if not for Gajeel. Are you saying that Laxus became a separate entity or a second personality came out. No that's not what happened, that's just Laxus' negative emotion getting the better of him and making him do irrational things, the same happened with Natsu when he was fighting Gray. His negative feelings arose due to Lucy's "death" and made him irrational. It's the same with Gray. They simply lost their rationality temporarily and wanted to vent it out on someone or something, this doesn't constitute to separate entities or second personality at all.

And this occurs in real life too. Don't you dare tell me that you haven't argued with your family members before for minor issues and think back why you argued on that later especially if you said or did something bad to them. It's the same as that, the negative emotions temporarily took over and made them irrational but that doesn't mean a separate entity or another personality is born or arisen.