User blog comment:FairyRaven/Fairy Tail Chapter 363: The Stories That Demons Read, Review and Commentary/@comment-8153438-20131210052643/@comment-24066070-20131211030637

Truth be told, I find this whole face thing being connected to the lives of merely 3 MC members a bit dumb. Both generations of the MC had members with apparently no magic power. On top of that most were already old. Therefore, I find it ridiculous that such a dangerous thing is connected to 3 defenseless old persons. After all, the MC may be the target of assassins who don't even know about face. Before you know it that face thing goes off because the MC got killed by random terrorist or even because these old geezers just kick the bucket. At least link that weapon to the Ishgar Gods or so.

That 100 year quest has something to do with Acnologia I think. Since that's pretty much the only thing that only the most powerful mages can challenge and considering he's still alive, that would explain why nobody accomplished it in a century. Besides, Gildarts did encounter the dragon on the quest, so it may have just been the target all along.