Chaos;Gate

Chaos;Gate (also known as ChäoS;Gate) is a Steins;Gate and Chaos;Head crossover light novel featuring two of its main characters.

The story was written by Naotaka Hayashi (the Steins;Gate and Chaos;Head visual novels' main writer). It was initially published in the Nitroplus Complete magazine released on September 30, 2009, 15 days prior to the initial release of Steins;Gate.

Synopsis
The story takes place one year before the events of Steins;Gate. Sena Aoi, while chasing a porter carrying a N.O.Z.O.M.I. Technology terminal in Shibuya, encounters a high school-aged Rintaro Okabe within the Shibuya Station. When Sena's calm and composed personality clashes with Rintaro's overtly pompous antics, sparks will fly...