User blog comment:B214/Shin DxD 1 discussion/@comment-29963364-20180803032716/@comment-34061653-20180803142755

Issei has been developing his power. In volume 22 He learned to use Psuedo DxD G which allows him to use a god-class form that doesn't have the drawback of ending his life. In volume 23, Partial DxD G was developed to use power beyond CxC which consumes less stamina than Psuedo DxD and in volume 25 he can now use Psuedo DxD G which has a longer time limit of 88 minutes with the addition of summoning Ddraig. So Ishibumi has beem developing Issei's power. In terms of mental developement, he had that in volume 23 when he lost Dulio. Ishibumi wanted Issei to experience defeat as a king and how he can recover from that. As far as leadership goes, he has showm promise in volume 9 against Cao Cao but the problem right now is he relies too much on Ravel and is still a novice at being King.