User blog comment:B214/Light Novel Volume 16 spoilers/@comment-162.202.198.72-20131019091326/@comment-9339850-20131019153404

maybe he'll be able to absorb some of their power's through the beams each girls breasts give, like for example Issei will get a small version of the PoD from Rias' boobs, and if the other girls get the Boosted Gear Gift, He will be able to use Holy Lightning from Akeno's breast etc. etc.