The ban on pornography did come about during the Meiji era but that action is widely viewed to be due to Western influence and anxiety among the ultra-nationalist
There's an interesting (if a little dry) paper on the emergence of hentai here but I think the gist is that during the Meiji period, heavy censorship was
here: http://www.hawaii.edu/PCSS/online_artcls/pornography/prngrphy_rape_jp.html This is a very interesting historical section: "The government of the Meiji