User blog comment:Jopjopjop/Volume 19 Spoilers/@comment-1.53.124.174-20150712141105/@comment-1359322-20150713002145

Even if the plot-line is almost similar, the focus isn't. Repetitive only occurs when plot-line is the same, main focus is the same, and the fights and everything are the same which is clearly not the case here. Yaegaki appeared in a neighboring town and his purpose was too kill Touji for revenge only not to fight DxD.

In V17, Rizevim was aiming for Agreas while Euclid is aiming for Rose. V18 & 19 which are actually one plot, they focus on the Heaven/Exorcist/Church side starting with how their past deeds are affecting present events and how their alliance affected their followers.