Nana Toshi Monogatari: Hokkyokukai Sensen

In the year 2099, a catastrophic shift in Earth's axis leads to widespread natural disasters and the near-extinction of humanity. From a global population of ten billion, only two million moon colonists survive. After three years of chaos, the survivors return to Earth, establishing seven new cities to begin repopulation. However, the moon colonists, fearing the potential threat posed by their former neighbors, construct a ring of defensive satellites. This orbital defense system effectively traps the newly repopulated inhabitants of Earth, creating a tense situation between the two factions. The anime explores the themes of survival, rebuilding civilization, and the potential for conflict arising from fear and mistrust in a post-apocalyptic world.