User blog comment:Jopjopjop/Volume 18 Spoilers/@comment-24053170-20140624001114/@comment-3965848-20140624200846

Issei pretty much helps the character to which the volume centers on, and it wasn't just the girls but the guys too such as vol 3= kiba and vol 16= Gasper. My guess is that vol 20 could be someone from Vali's team.