User blog comment:B214/Question and Answers 6/@comment-207.96.205.3-20160725195804/@comment-9595671-20160726023640

At the very least, I'm pretty sure he's gonna enlargen the girls with smaller breasts who are in his harem. I recall in EX it's mentioned all of Issei's harem have big breasts now, enough that their kids thought that breasts were big by default at one point. The question is if we'll actually see it when it happens.

Even if the girls who are already busty do end up growing, it'll probably be so little it's not really any difference. After all, most of the girls who are already busty are the older members of the harem who are either nearing or have already stopped growing by this point.