Seems to me that your friend's limitation of "only hentai" is depriving the paper of worthwhile information. I mean, in my experience hentai anime in general is low budget and poor quality, and for god's sake it isn't worth doing a serious paper on. I'd probably kill myself if I had to actually do research on the 90% utter crap that is the anime hentai genre. And in any case, like any other genre of anime, in the end the genre almost always comes down to one or two groundbreaking "father" shows from which all otheres are copied and plagarised (and most done badly at that), and many of those "father" shows aren't hentai themselves.