Cross Days is a Japanese erotic visual novel developed by 0verflow, released on March 19, 2010 for Windows and later ported as a DVD game and for the PlayStation Portable (PSP). The story, a dramatic slice-of-life, follows the life of Yuuki Ashikaga, a high school student who becomes the ambivalent love-interest of two girls during his second term, and the effects this has on himself and his relationships with other characters. Though the game requires little interaction from users, Cross Days engages the player through a nonlinear plot that they are given opportunities to change the course of during play. The game is the third installation of the School Days line of series, succeeding Summer Days.
0verflow announced work on Cross Days in December 2008. From February 2009 to March 2010, the game was postponed a total of six times, going on to perform marginally-well upon release. In the weeks following this, after it was illegally found on peer-to-peer (P2P) networks, a trojan horse disguised as the game was released, publishing the personal information of unknowing users online for public access.
Following the game's release, Cross Days made transitions into other media: a manga was serialized in the Kadokawa Shoten magazine Monthly Comp Ace from April 26 to August 10, 2010; three light novels were published from September 15 to October 29, as was a strategy guide; a radio drama was broadcast during development; and the game's original soundtrack was also published by Lantis from April 24 to July 21.