User blog comment:B214/Question and Answers 6/@comment-90.202.240.151-20161009210010/@comment-202.80.212.147-20161010120318

ishibumi said that DxD G is most likely to be Issei's last power up. So, i think in this arc Issei will just find a way to train his body and make a good use of his other powers like Wyvern and etc