User blog comment:FairyRaven/Fairy Tail Chapter 435 & 436: The Cry of Victory & Memoirs, Review and Commentary/@comment-7418318-20150522195321

This last chapter made me think of Natsu's scarf again.

Could it be that the scarf might not be from Igneel, but actually from Zeref only given to Natsu through Igneel?

Considering how Zeref didn't want to kill people (at least some of the time), I wouldn't be surprised if he tried to find ways to block his magic from killing. Protective items for people near him seem a good idea. Could the scarf have been a failed attempt to build exactly such a protection.

I call it failed because it only protected Natsu once and all the negative energy it absorbed even prevented Wendy from healing him. In practice this probably means the scarf will block one death wave and then lose it's protection until it's cleansed... so not very useful to stay close to Zeref for a prolonged time.