User blog comment:B214/Question and Answers/@comment-108.17.150.138-20130717185525/@comment-16075832-20130717192718

True, but I believe the group will reunite in the volume and something will go down with the vampires. Hopefully we get to see the effects of Rias' new move in action. I also want to see Kiba improve his Glory Drag Trooper.

Issei uses a new ability in every (main) voulme so I can only assume he'll either get a one time power up (like volumes 7 and 12) or he'll learn a new ability. I think volume 3 was the only volume he didn't display anything new, but I might be mistaken. I think there was something about sensing a foe's power level or something.