Portus features story and art by Jun Abe.

Asami Kawakami is a 17-year-old high school girl and a member of her school's art club, which is run by her friend and adviser, Keigo Sawa. For some time, her best friend Chiharu hasn't been answering her cell phone and has also stopped coming to school. One day Chiharu shows up at the art club and says that the reason she was gone was because of a video game, and that she has also seen many horrific things.

That day, she goes home and under the mysterious influence of the game, commits suicide. Asami goes to Chiharu's room after her death and finds the video game, Portus, and takes it home in the hope of finding out what it is about this game that made her friend commit suicide.