Two hundred years ago, Yokohama Station, which had been under constant construction, developed the ability to self-propagate. Now with nearly all Honshu, the mainisland of Japan, consumed by the growing station, the population has been split into two groups: those who live inside the sprawl with fare cards embedded in their brains and the few who persist on the remaining scraps of untouched land. Hiroto has lived his whole life on the outside, but when an exile from the station entrusts him with a mission and a ticket, he ventures into the ominous belly of the beast for the first time...