User blog comment:IamJakuhoRaikoben/Chapter 370: Demons Reincarnated, Review./@comment-1359064-20140207151624/@comment-4829046-20140207152936

Technically, he didn't really name those arcs in the titles. This one he named them starting from the prologue. I think its a way of staying in-line with the "Book" element first made clear by Cobra. What with all this talk of Demon books and Sayla's constant use of story.