User blog comment:B214/Volume 23 discussion blog/@comment-206.224.253.186-20170420231523/@comment-31137559-20170421001553

Well what more does he need? He's already at the level of Satan-class devil after only a year. Would Sirzechs be a Super Devil without his Power of Destruction? Would Dulio be Seraph level without Zenith Tempest? You have to consider that the Boosted Gear was the only thing special about Issei at the beginning of the series. He already uses demonic powers such as when he uses Dragon Shot, Dragon Blaster, and Crimson Blaster. Those are basically concentrations of his demonic powers. And also Issei being able to breathe fire is his demonic powers. What will learning Norse magic do for Issei?

Why shouldn't Issei depend on his Sacred Gear? Should Dulio stop depending on Zenith Tempest when it's the strongest thing he has? Issei's Boosted Gear is his main weapon at his disposal. If someone like Rizevim does come in the future, Issei has Penetrate and plus he's going to be a Super Devil.

I thought it was a good idea at first for Issei to train his body like Sairaorh to the point where he becomes competent without his Sacred Gear. But we have to consider that Issei builts up his stamina and power every day in his Boosted Gear. That is also making him way stronger in his regular form as well.