Nana Toshi Monogatari: Hokkyokukai Sensen
English title: Seven Cities Story: Arctic Front
Japanese title: 七都市物語 ～北極海戦線～
Type: OVA
Episodes: 2
Source: Novel
Genres: Drama, Sci-Fi
Studios: Studio Junio
Producers: animate Film, Sony Music Entertainment
Duration: 29 min per ep
Rating: PG-13 - Teens 13 or older

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)