The Earth was left behind by humanity in order to preserve it and now, they reside in a massive circular edifice that hangs 35 kilometers above the planet. One's position here determines their social status; the higher the floor, the greater the prestige. Mitsu is a young man who just graduated junior high school, and his father used to work as a window cleaner. However, Mitsu is forced to take over his father's job when he goes missing and is believed dead. Through this new occupation, Mitsu gains a distinct viewpoint on the living conditions in the Saturn Apartments.