Code_18 is a visual novel video game developed by Cyberfront and released on September 29, 2011, for the PlayStation Portable and Xbox 360, and later for Microsoft Windows.

The story follows Hayato Hino, a high school student who receives voice messages from the future on his phone, and is stuck in a loop, repeating a month of his life over and over again.

As with the rest of the Infinity series, Code_18 is a visual novel in which the player makes progress through the linear story by talking to characters and listening to dialogue.

[1][2] The state of Hayato's romantic relationships, together with choices made during the story, can alter the flow of events to a degree; some options can trigger alternative bad endings for characters, and the game's full ending is altered depending on whom Hayato has formed a romantic relationship with.

When Hayato is about to test his "Dragon Unit" flight pack on the school's roof, a girl falls from the sky, wearing a similar device.

Ryuusei Academy and the Second Science Club prepare for a school festival that is scheduled for a month later, when Hayato's science professor, Genkuro Kanbara, gives him a smartphone chip composed of an "Agastia Stone", which theoretically would allow him to receive voice messages from the future.

At one point, due to an accident with the Dragon Unit, Hayato's house blows up, forcing him to sleep in the science clubroom.

During each loop, he gets closely involved with one of the game's female characters, helps them with the festival, and with resolving their personal problems.

As the time machine only works in a zero-gravity environment, they combine it with the Dragon Unit and take it to the 1,200 feet Sky Tower; their way there is hindered by an earthquake, however they are able to reach it with the help of Hikari, Tamaki, Yuzu, Nanari, and professor Kanbara.

The Hayato of 2040 then sent voice messages to his 2018 self to offer guidance and to cause an ontological paradox, ensuring Akari's continued existence.

Initially, the development team had planned to use the "escape" theme, but had to change it due to concerns about the size of the audience for the game.