User blog comment:B214/Volume 21 info & spoilers/@comment-28087053-20160424011718/@comment-1359322-20160424035049

The author never said that anyone who uses DxD will die for sure. In fact from Ophis' downgrading DxD G, it's more to that Ophis didn't know how much power to unlock/bless to Ise in Volume 20, hence Ise ended up in that state.