User blog comment:B214/Shin DxD 1 discussion/@comment-2607:FB90:3851:A5D3:0:14:ECCB:7501-20181029115052/@comment-2601:87:8300:20D0:5543:CD45:A7F7:DF0D-20181029124509

Maybe to put it simply it's like a disciple trying to surpass the master. In order to move he must surpass her. Issei is not only in love with Rias but indented to her from very beginning. He wants to prove to her, to everyone, but more importantly to himself that he is worthy to stand by herside. He promised the future to her and now is the time to show it.