User blog comment:B214/Question and Answers 6/@comment-24098614-20190617190922/@comment-5384276-20190619230105

A combination of Asia's late growth spur & her demonic powers being subconciously used to enhance her growth. Her desire to be seen as attractive to Ise is causing her to become more well endowned. Remember, she would always get jealous when Ise was being seduced by Rias & Akeno ude to their breasts.