Google hentai. Manga is Flash Gordon. Hentai is Flesh Gordon with a chainsaw.
Trust me I know what hentai is - I’m an anime/manga fan and I need to know how to avoid hentai, yaoi, yuri, and other lovely stuff like that.
Not saying that it should be in a library at all, but if the kid stole the book from the adult section, then I think he and his mom are more to blame than the library.