Auckland Libraries has a separate categorisation for "erotic comics" which contains 36 titles.
It shows explicit sex scenes featuring Stix.
The Herald cannot print the content of the comic, even though the comic can be displayed on the shelves of the public library.
Auckland Libraries general manager Mirla Edmundson said the all libraries contained material which might offend.
"We would really defend the right of people to read whatever it is they wish to read. The difference with graphic novels is that they are by their nature visual. With a graphic novel, there isn't a lot of time between seeing the image and understanding the content."
While the library occasionally kept material behind the counter, it wasn't considered a solution.
"We would forever be debating what should be behind the desk."
She said there was a degree of "viewer beware" when it came to sampling titles in the adult section of the library.
Dylan Horrocks, graphic artist and author of the acclaimed Hicksville, said Perverts of the Unknown showed author Brandon Graham at an important part of his development as an artist.
"I'm delighted it is in the library's collection because it's a significant part of what's happening in comics at the moment. Graphic novels are always vulnerable to moral panics around these books because people find pictures much more confronting than text."
Earth's End Publishing editorial director Adrian Kinnaird - a champion of New Zealand comics - said author Brandon Graham was a "highly regarded cartoonist", he said.
"While erotic or pornographic comics aren't for everyone, like any form of literature I believe they deserve a place in the spectrum of comics storytelling, alongside any other graphic novel on a bookshelf."
Kinnaird said comics had fought for decades a stigma that they were a "medium exclusively for children" despite titles showing its maturity. He said "this perception continues to be pervasive and as a result graphic novel sections in libraries around the world have at times been subject to censorship of certain titles".
"Comics are a visual medium, and that's a very powerful form of communication, which can elicit a variety of responses from a reader."
Auckland councillor Ross Clow said the images shocked him.
"They're pretty out there, that's for sure. I think that's over the top and there's no question about it. I think it's unsuitable for any unsupervised section of our libraries."
Fellow councillor Linda Cooper said she was taken aback when first confronted with the images. "It's kind of what you expect in a porn movie but it's in a book.
"I wouldn't have expected to see that in a library but there is that balance - it's not illegal, it's not in the children's section and if you don't like it then don't go looking for it."