Takuya Arima receives a package from his missing father, a historian who vanished without explanation, containing a letter describing parallel worlds and a device that can travel between them. Convinced his father might still be alive somewhere across those dimensions, Takuya starts investigating with the device's help, drawing in the people around him: his stepmother Ayumi, his homeroom teacher Eriko Takeda, the journalist Kaori Asakura, and his former teacher Mitsuki Ichijou, as the boundaries between worlds start to blur. This manga adapts the original visual novel.