A city mysteriously vanishes one day. Takuya, a professional by-the-contract courier and lone wolf, encounters Yuki, the city's last survivor. The two rely on a message from Yuki's father, who was reported missing, and travel to the vanished city of Lost. Unexpected difficulties, however, stand in the way of the relationship, with the reality especially surprising for Yuki. Before them are the emotions of people who have been left behind, as well as a mystery gang operating in the shadows and revealing the secret scheme. Takuya and Yuki, who were initially strangers, would become closer on the voyage as they unraveled the mystery of the Lost City.