Hayashi Renei, a seventh-grade student, is disturbed by a recurring dream where her deceased brother, who passed away in a car crash, is reincarnated as Coo. The dream persists every night and leaves Renei distressed. Coo's world is incredibly harsh, surpassing the cruelty of the real world, as it is filled with agony, misery, and unhappiness. Renei aims to find her way back to reality with the help of her brother and newfound friends in Coo's world. Her ultimate goal is to escape the realm of the dead and return to the land of the living.
