Nana Toshi Monogatari: Hokkyokukai Sensen

By 2099, Earth's axis has shifted, causing it to rotate at a 90% angle relative to its previous equator. This leads to three years of widespread natural disasters. Afterward, the planet's population drops from ten billion to just two million, all of whom are former moon colonists. Some of these survivors return to Earth to start rebuilding in seven new cities. The remaining lunar residents, however, worry that the returning Earth inhabitants could be a danger and set up a network of defensive satellites to contain them on the repopulated planet.