User blog comment:B214/Volume 22 spoilers/@comment-78.8.41.88-20161017150638/@comment-86.141.160.246-20161018164719

I think that Issei and Vali are going to use different ways to make their powers stable. I think Vali will choose to master his power with his magic skills while Issei will choose extreme training until he gains control over his body and its energy.