Developer Spike Chunsoft launched the Japanese-language iOS port of the game, which was originally released in December 2009 on Nintendo DS in Japan, last May. Known as 999: The Visual Novel, the mobile version lacks the puzzles that were present in the original DS title; it plays out as a visual novel, with speech bubbles like the ones in comic books instead of pages to turn.
According to the game's website, 999: The Visual Novel requires iOS 5.1 or later and is optimized for iPhone 5, but will also be playable on iPod touch and iPad. The iOS port features higher-resolution art that's suited to iOS devices' displays, as well as a flowchart that will let players jump around the story.
999 is the first game in a series that also includes the 2012 follow-up Zero Escape: Virtue's Last Reward and a third game that is currently on hold.