User blog comment:Jopjopjop/Volume 18 Spoilers/@comment-99.170.116.67-20150118015721/@comment-24468758-20150118191021

But if penetrate even works on Raiser's flames he is very likely to lose and the short story "The unresurrected Phoenix" has some kind of fight between them in which Issei was able to drain Raiser's stamina enough to considerably weaken his healing ability (though Raiser still needed to recover completely).