"Yokohama Station SF" is a science fiction manga series set in a dystopian future where Japan has been overtaken by an autonomous, self-expanding structure known as Yokohama Station. The station, a sprawling and seemingly sentient entity, has engulfed most of the country, integrating itself into cities and landscapes. It operates under its own rules, issuing "Suika" cards to inhabitants, which serve as identification and currency. Those without a Suika card are considered outsiders and are expelled from the station's territory.

The story centers on Hiroto, a young man born outside Yokohama Station in the unincorporated areas of Japan. These regions, known as the "Outside," are harsh and lawless, with inhabitants struggling to survive. Hiroto carries a mysterious implant in his body, a relic from his father, which grants him unique abilities but also marks him as a target. Determined to uncover the truth about his implant and his father's past, Hiroto ventures into the station's vast, labyrinthine interior.

Inside Yokohama Station, Hiroto encounters a society governed by the station's rigid systems. The station's inhabitants live under constant surveillance, with their lives dictated by the Suika system. Hiroto meets various characters, including Nagiko, a young woman who aids him in navigating the station's complexities, and Enoshima, a researcher investigating the station's origins and behavior. Together, they uncover secrets about the station's creation, its purpose, and the role Hiroto's father played in its development.

The narrative explores themes of autonomy, control, and the consequences of technological advancement. As Hiroto delves deeper, he learns that the station's expansion is not merely a physical phenomenon but also a reflection of humanity's reliance on systems that dictate their lives. The series blends action, mystery, and philosophical inquiry, presenting a world where the boundaries between human agency and artificial control are increasingly blurred. The characters' journeys highlight the struggle for individuality in a world dominated by an omnipresent, impersonal force.