User blog comment:B214/Question and Answers 6/@comment-82.2.190.195-20161102162156/@comment-1359322-20161102174622

That doesn't really mean much like i said, the servants themselves will have to improve themselves. Issei's Dragon aura might play some role actually seeing how Xenovia and Rose never got any chance despite spending time with Issei for so long, the existance of the effect is kinda doubtful.