Nana Toshi Monogatari: Hokkyokukai Sensen

Earth has thrown off its axis and starts rotating at a 90-degree angle to the equator of the 20th century in 2099. Natural disasters continue for three years, and when things finally calm down, only two million moon colonists are left after Earth's ten billion people have perished. The remaining colonists of the moon worry that their former neighbors might pose a threat and build a ring of defensive satellites to confine them on the recently repopulated homeworld while some return to start the repopulation of the world in seven new cities.