One day, a city is destroyed. Takuya, a lone ranger courier, and Koyuki, the only girl who survived the destruction. The two began to travel to the destroyed city based on the message from Koyuki's father, who was thought to have disappeared. However, unexpected obstacles appeared in front of them. It was a reality that was too shocking for Koyuki - the longing for the survivors, the mysterious organization active in secret, and the hidden conspiracy. Takuya and Koyuki, two people who had never met before, gradually deepened their relationship as they traveled, and gradually approached the mystery of the destroyed city.