User blog comment:B214/Volume 22 spoilers/@comment-50.139.232.230-20160721023809/@comment-4547267-20160721061852

Well if you think about it make sense Issei take Asia and Xenovia because, like B214 said, he need to make special bonds with his teammates to make them stronger, which he did. Face it, the Chruch Trio maybe very close to Rias like a big sister, but Issei is the one who help them out the most and has a deeper bond, just like how deep the bond Rias has for Akeno, Kiba, Koneko, and Gasper because she saved them from danger like Issei did for Asia. And beside, the tournament was coming soon and he was short on teammates, he needed this because he and Ravel wanted to test out how strong they team could be and what weakness they need to cover over. It was actually smart of them to start with weaker teams because they need to see how far they teamship can do