Anzu Natsuno is the leader of the triathlon team of her all-girl High School. One evening she hear a voice singing and following the voice, she finds her close friend Kana in a High School hall, and Kana commits suicide. Anzu, nor any other girl of the team can understand why Kana did it. The girls soon begin to investigate. At the same time, reporters of the independent magazine "Masaka" heard the rumour of an "infectious song" that will drive to suicide to anyone who dares to sing it. Reporters Riku Nagase and Taichi are assigned to the story, they go to Kana's funeral in order to know if this is just another "urban legend". There they meet Anzu, and Kana's childhood friend Shuri, member of the pop group "AKB48". At first Anzu doesn't want to talk to Riku and Taichi, but Shuri got interested and wanted to know what happened to her friend, so she joins the reporters. Both Anzu's triathlon team of girls, and "Masaka" magazine reporters, with the help of Shiru start to follow the leads to uncover the truth, while more suicides began.