This series happens in the world of Freedom Project
When the people saw, that the Earth was done for, some went for the moon, some went underground. The scientists among Patema's and Age's ancestors at one hand build the underground, where Patema's (maintenance crew) and Age's (living quarters) people live and on the other hand wanted to invent the means to defy gravity (NOT with brooms, for Kumbricias sake!!) and allow a more energy-efficient evacuation to the moon for more people. The experiment was a great disaster, the very disaster, that caused Age's people to become inverted. The condition of the environment worsened more and more and the people of both habitats isolated themselves from the outer world, waiting for the ecosphere of Earth to regenerate (that's why the place Patema strolled into was called the "danger area": it was the transfer area to and from the poisoned environment of the Earth surface). Many, many years after that, Earth's environment was again, more or less, on its feet and could even support human life. Eichii, Age's father, discovered the truth, not only about his world being the real inverted one, but also about the moon colonies and wrote it in his journal, together with the exact principles of the anti-gravity devices the scientists of the disaster developed and was murdered by Izamura for that, together with Lagos, his best friend. In the future, Patema, Age and their family will complete the work of the scientists of the old era, help rebuilding the civilization on the Earth surface (the level of technological development of the underground civilization is about that of the end of the 20th century), restore Age's people and their stuff to their correct gravitational polarity, build the spacecraft based on the anti-gravity drives the scientists developed without repeating their mistakes and make an important contribution to re-unite humanity of the underground, surface and moon. Age's and Patema's children will be the first settlers on the new colony on Mars. Jii was not surprised by this at all, since the village elder made him the regent before his death, so he may prepare Patema for her role as queen. The events of Sakasama no Patema is set 40 years prior to the events of The Big O
Think about it: the ceiling structure above the Agian surface world is similar to the one above Paradigm City. Perhaps it's even the exact same one. Meaning, the people of Paradigm City are really inverts. This was the harsh truth that was forgotten 40 years ago. The Agian government eliminated the few who discovered this, then covered it up by building the Domes and spread propaganda that there was no civilization beyond them, to keep anyone else from growing curious.In time, that very revelation would be what drove Schwartzvald to insanity and open his eyes to the truth. That the the citizens of Paradigm City were the uninformed masses who'd been lulled into a false sense of reality by their government and that their "great city" was a sham. Nothing more than a jar deep beneath the Earth's surface, to keep them from suffering their ultimate fate of being swallowed up by the sky - like all "sinners" were destined to be.
Arriving at that realization is what eventually lead him to find Big Duo and with it, he attempted to reach the surface world so he could see it with his own eyes. Just as Patema and Age had done 40 years ago.
