358/2 Days was developed by h.a.n.d., with Square Enix employees overseeing the process. The game was directed by Tetsuya Nomura and co-directed by Tomohiro Hasegawa. In 2007, Nomura mentioned he wanted to do a spin-off Kingdom Hearts game on a mobile platform and wanted the game to play slightly different from the other titles already in the series. 358/2 Days was announced alongside Kingdom Hearts Birth by Sleep and Kingdom Hearts coded at the Tokyo Game Show on September 20, 2007, where a trailer was shown in a photo-prohibited theater. New trailers were shown and a playable demo was available at the 2008 Jump Festa in December 2007 and the DKΣ3713 Private party in August 2008. Both single player and multiplayer demos were featured. Xion was also shown in the new trailer and in the multiplayer demo.
