Some time after the events of Gundam EXA, Sthesia Awar informs Leos Alloy that she discovered a new GA data cluster from a computer outside of Jupiter X. The two dive into the new data and find themselves in the Universal Century, during the attack on Side 7. However, after entering the colony, they find that the inside was in ruins, and the RX-78-02 Gundam has been destroyed before it could be activated by Amuro Ray.

The two discover a faint life sign in the colony, the source of which is Themis Chiron, a G-Diver from Saturn II. Chiron warns the two to get away as soon as possible, or they would be caught in the conquest of Mars I.

(Source: Gundam Wikia)