The story takes place in unnamed timeline, where humanity has highly advanced technology. However, the human population is decreasing and it seems that they're on their way to extinction.

The protagonists are Leos Alloy, Sthesia Awar and their Haro. They work on a Jupiter base called "Jupiter X", using "General Answer" (or "GA") which contains a massive repository of data about the alternate history of Humanity, Leos travels to the Earths' of the alternate timelines in an effort to collect data that might give them a hint for the evolution of mankind.

(Source: Gundam Wikia)