17-year-old high school student Asami Kawakami's friend, Chiharu, has stopped answering her phone and never comes to school anymore. She would rather spend her time playing Portus, an old videogame. There is an urban legend that there is a secret level where a boy appears and asks if you want to go to the other side. If you say yes, you die. When Chiharu cuts her own throat, Asami and the art club teacher, Keigo Sawa, set out to find out the truth behind the legend and Chiharu's suicide.