User blog comment:B214/Volume 17 spoilers./@comment-1359322-20140311050948/@comment-16281343-20140311061226

Well, they definitely need another Volume. After Volume 10 (Rias) and Volume 7 (Akeno), nothing much happened between them and Issei.

As for Kiba, development between him, Tsubaki, and Gram is a must.