The story is set in a near-future Earth, in the aftermath of a major disaster that shifts the planet's polar axis 90 degrees, situating the poles along the equatorial line and killing everyone on Earth. A moon-based colony avoids the disaster, and begins recolonizing the depopulated Earth by establishing seven cities in strategic locations. However, to ensure the loyalty of the Earth colony, the moon establishes an orbital defense system that destroys anything that flies 500 meters in the air. When an unknown virus kills everyone on the moon, humanity becomes trapped on Earth, where the political intrigues of the seven cities continue to play out.
 
(Source: Anime News Network)

In 2099, Earth has shifted off its axis and begins to rotate at an angle of 90% to the 20th-century equator. Three years of natural disasters follows, and when things settle down, Earth's ten billion population has died and only two million moon colonists remain. 
Some return to begin the repopulation of the world in seven new cities and the remaining colonists of the moon fear that their former neighbors might pose a threat and construct a ring of defensive satellites to trap them on the newly repopulated homeworld. 
(Source: AniDB)

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