User blog comment:Crimson and Darkness/Volume 25 discussion blog/@comment-95.210.189.106-20180409160625/@comment-28884330-20180410230255

Vali is the guy who has wanted to defeat Great Red since the very beginning of the series. If Issei becomes stronger than him it will only make him more excited and hyped, and the stronger Issei becomes the better for Vali.