User blog comment:B214/Volume 22 spoilers/@comment-50.139.232.230-20160808093804/@comment-95.90.227.243-20160808141901

But unlike Issei Vali cannot reach the same high as a Dragon as issei but he can reach a high as Mou but it will be under Issei. Issei (a little true Dragon with almost infinity Potential ) and Vali (a True Lucifer with more potential as the current Mous but under Issei) And i think Issei will ask Raziel to join ExE !