User blog comment:Jrotc193/Job requests/@comment-4829046-20130602184404/@comment-4829046-20130602184742

Or perhaps to capture the loch ness monster kind of thing?

Maybe the job Gildarts went on was to remove Acnologia's presence from somewhere as that was where he was living for the last 100 years and he had just been killing every human that came near his resting place. After Gildarts fought him, he probably moved elsewhere to do something, and that is the reason Gildarts survived and failed the job and claimed Acnologia left.