Losing steam after initial popularity is probably a secret nightmare every artist has about their first successful piece of work. If "Attack on Titan" creator Hajime Isayama ever worried that after the first few volumes that fans would lose interest, he can probably rest easy.

After all, 17 volumes later, the series is still making bestseller lists.

Amazon Japan has revealed their top 10 bestselling manga volumes for the year of 2015. Though the number one spot was not held by the "Attack on Titan" manga series, volumes 15-17 took up three out of the other spots on the list, concluding that at least among Amazon Japan shoppers, the "Attack on Titan" manga volumes are still very popular.

Despite the extreme popularity, Hajime Isayama still seems to be in a state of disbelief. In a November 2014 interview with Brutus Magazine, the author mentioned that he never imagined that the "Attack on Titan" manga series would become a world-wide phenomenon.

"I knew that making a living from drawing manga is extremely tough, so my dream back then [when he was 19] was just to make enough to feed myself with my manga, even if it never became a big hit - let alone the idea of becoming a millionaire," said Isayama (via Mangabrog).

In fact, Isayama in particular detested the idea of making a series popular by using market research or trying to appeal to fans.

"I was repelled by the sort of manga that's based on marketing research about what sort of characters or plot elements will be popular with readers. Relying on that stuff, you'll never make anything new. So then I took that desire to see someone do something new and decided to try it myself," he explained.

In addition to being an extremely popular manga series, "Attack on Titan" has been adapted into an extremely successful anime series, two live action movies, two anime films, and live action TV series. On top of this are several spinoff manga series, anime OVAs, and recently a light novel adaptation.

Though some might feel "Attack on Titan" is close to the saturation point, there's no doubt that there's still plenty of fans wanting to know the fate of humanity in the face of titans.