One day, a city suddenly vanishes. Takuya, a freelance courier and lone wolf, encounters Yuki, the sole survivor of the city's extinction. Guided by a message from Yuki's father, who was reported missing, the two set out for the vanished city, Lost. Yet, unforeseen obstacles confront the pair, with the reality proving particularly shocking for Yuki. They face the emotions of those left behind, a mysterious group operating in the shadows, and the exposure of a hidden conspiracy. Takuya and Yuki, initially strangers, strengthen their bond throughout the journey and uncover the mystery of the Lost city.