Kodansha’s Attack on Titan manga, a shonen title by Hajime Isayama, is a major hit in Japan, with over nine million copies sold according to Sports Nippon via Anime News Network.  Eight volumes have been released in Japan. 

The title has been flying under the radar here, with under 400 copies of the first volume sold in comic stores (see "Top 300 Graphic Novels--June 2012"), and no Top 20 appearances on BookScan’s monthly Top 20 Graphic Novel charts (see "BookScan Top 20 GNs Index"). 

But its Japanese sales are worth noting, if only to indicate a title that might catch on if it had higher visibility.