After the events that took place in Exit Music, the protagonist and Natsuki come back to life with the help of a mysterious incorporeal entity, in order to be subjected to a test; find the culprit of their fateful demises and put an end to him. One life in exchange for two, with the handicap of having limited time and limited attempts. If they succeed, they will have a second life on Earth. If they fail, they will die for good and will never see each other again. On the way they will suffer multiple inconveniences, both fortuitous and intentional, but they will put on the table all the means at their disposal to solve a mystery that surpasses them in all aspects; because they do not understand neither the random reason why they have been entrusted with such a mission, nor the way in which they will be able to achieve such an elusive and apparently impossible purpose.