All I can say is their branch of the library must have a heck of a lot more cash than mine here in the south part of the county, I can’t find new science fiction on the shelves let alone hentai. Sheesh.
Anyway without knowing what the manga is I’m not sure it would be hentai. It’s possible it’s one of the more disturbing graphic novels that aren’t sexually explicit - there are plenty of those. It’s sort of an important detail...