User blog comment:B214/Volume 23 discussion blog/@comment-31764731-20170418200747/@comment-31137559-20170419111329

As far as we know Issei will never surpass Shiva. Having the power of the two strongest beings is very different than being those two beings. And Issei doesn't really need another sensei or anything. He's already powerful enough and is going to get even more powerful. I don't know what Shiva is trying to get out of Issei by trying to drag him into his conflict.