When his clan is wiped out by a beautiful demon, young Taikobo finds himself in charge of the mysterious Houshin Project. Its mission: find all immortals living in the human world and seal them away forever. But who do you trust—and whose side are you really on—when you've been trained to hunt demons by a demon?

Mobius is a perfect digital world for the imagined benefit of humanity by μ, a virtual idol program that attained sentience and self-awareness. Only humans who are suffering in the real world and strongly relate to μ's songs are lured into Mobius. Once they enter, people often forget that the real world exists. Regardless of age or gender, they are turned into students and forced to experience school life over and over, which μ considers "the most radiant time in a person's life."