In AG 108, the colony, Ovan, was attacked by the UE and destroyed. Flit Asuno survived the attack, received the AGE Device from his dying mother and went to Nora to begin constructing a mobile suit called Gundam.
In AG 115, Nora came under attack. It was then that Flit activated his AGE-1 Gundam AGE-1 Normal and destroyed a UE's ovv-f Gafran. UE, learning of the Gundam, sent in their colony destroyer to destroy Nora. At the same time, all Nora colonists evacuated to the colony's ejectable port and it was pulled out by Diva (under the command of rogue captain Grodek Ainoa). While the Gundam fought the UE forces outside the colony, a debris prevented the port from being evacuated. Commander Hendrick Bruzar of Nora's Arinston base then sacrificed himself by blowing the debris in a suicide attack.
Later, Diva traveled to Fardain. There, Flit faced the ongoing battles between the remnants of Euba and Zalam, whom still fought each other even though the war has ended. During the skirmish, UE's ovv-a Baqtos came into the colony and Flit fought against it, but ended up being out powered by the much stronger Baqto and being captured by Zalam's CMS-223Z Zila, thinking the Gundam AGE-1 Normal as an enemy trespassing in their territory. While Flit kept convincing Don Boyage, the leader of the local Zalam forces to fight UE, leader of Euba forces Ract Elfamel, came for payback. Again, in the middle of the battle, the Baqtos came back into Fardain. Flit managed to convince Zalam and Euba forces to cooperate against the Baqtos and he himself headed back to protect a truck from the Baqto. It was then, the AGE system created the new equipment for the Gundam, which was later called the AGE-1T Gundam AGE-1 Titus. With it, Flit managed to defeat one of the Baqtos, while the others were defeated by Woolf Enneacle's new WMS-GEX1 G-Exes. After the battle, Zalam and Euba came to a temporary truce to protect Fardain.
When Diva was leaving Fardain with several Zalam and Euba warships, they faced a UE's battleship. Zalam and Euba mobile suits were no matched for UE's mobile suits, and Diva had to deploy their forces to destroy the enemies units. In the middle of the battle, Woolf and Flit faced a black transformable MS, xvv-xc Zedas which had previously appeared during Nora's evacuation. Zedas tricked Zalam and Euba mobile suits into hitting each other with its fast movements. Don Boyage, inspired by Flit's words of fighting together, decided to sacrifice himself to ensure both Zalam and Euba forces worked together with Diva forces to protect humanity. Also in the battle, the AGE system produced yet another new equipment, the AGE-1S Gundam AGE-1 Spallow, which was able to match the Zedas's speed. The UE forces eventually retreated, while the Diva and Euba-Zalam Alliance (now under Ract's command) travelled to Minsry to gather the remaining Euba and Zalam forces.
In Minsry, the Special Detachment forces under command of Stoller Guavaran of the Earth Federation Forces (EFF) 8th Space Fleet was tasked to arrest Grodek and Diva for discipline violation. However, the 8th Fleet came under attack by UE. Diva and the Zalam-Euba forces protected the 8th Fleet and forced the UE to retreat. The 8th Fleet then let the Diva go to "protect the humanity". Once Diva arrived at Ambat, each sides launched their mobile suits. This time, Diva, Zalam and Euba forces were equipped with more effective weaponries and managed to defeat UE's mobile suits. Grodek then gave the order to fire Diva's new Photon Blaster Cannon, installed by Mukured Madorna and created based on blueprint from the AGE Builder, and destroyed the UE Mothership. At the same time, Flit faced xvb-xd Farsia piloted by Yurin L'Ciel whom was forced by Desil, who also joined the battle. When Flit's Gundam AGE-1 Spallow was heavily damaged by Desil's attacks and was about to be destroyed, Yurin sacrificed herself. In rage, Flit crushed Desil's Zedas, but showed him mercy because of Desil’s tearful pleads. Flit then changed to Gundam AGE-1 Titus to open the Ambat's dock for Diva before changing back to Gundam AGE-1 Normal.
Inside Ambat, UE's footmen fought against Diva's footmen for their last stand while Flit, with his X-Rounder ability, defeated Geera Zoi's xvm-gz Defurse. Flit shoots at Geera, who's surprised to see that Flit is a boy. Grodek's team enters the control room, and he orders all the operators to surrender, but they ignore him. Geera enters the room and tells Grodek his threats are useless because they don't fear death. Flit enters the room, and when Geera removes his helmet, they're surprised to see that he's human. Flit says they may look human, but they're not because they killed innocent people. Geera comments that Earthers are foolish, but Grodek refers to him as Yark and tells him to shut up. Grodek says that as Yark, Geera has been sowing dissent and rebellion across the Earth Sphere. But in his investigation into the UE, Grodek found that Yark was present at Angel 14 years ago, so he must've let the UE mobile suits in to attack. Grodek says that Geera took his family away from him, so he's come all this way for revenge, which Geera thinks is sad. Grodek asks Geera what he's righting for, so Geera declares that he'll reveal who the UE are.
Woolf searches the interior of Ambat on foot and finds an injured UE soldier, and he's shocked to see it's a human. Geera explains that 150 years ago the Earth Sphere was overpopulated, so the EFF initiated the Mars Colonization Plan, known as the Mars Birthday. The EFF constructed 16 experimental space colonies in the Mars Sphere and sent settlers to live there. However, the Mars Rays created by the planet's magnetic storms caused a deadly disease that killed 20 percent of the population. Millais says all the settlers were wiped out by the disease, but Geera says that's a lie created by the EFF, who abandoned the Mars settlers. Geera explains that the survivors created a new nation, Vagan, so that they could eventually return to Earth. Grodek says that what the Vagans are doing is just a war of revenge, but Geera counters that Lord Ezelcant has much higher aims than that and that his plans are beyond their comprehension. Flit points his gun at Geera and says he doesn't care what their plans are because he can never forgive them. Meanwhile, Woolf holds the dying Vagan soldier in his arms, who gives him a locket.
Flit, feeling angry over the death of Yurin and his mother, wanted to shoot Geera but Geera was shot by Grodek instead. Arabel Zoi, having found out his father was mortally shot, wanted to avenge his father, before being haunted by Grodek's word. After Geera threw out his last breath, the remaining forces set off a self-destruct mechanism to blow up Ambat. Diva's crew managed to return to their ship in time and rendezvous with remaining forces and evacuated Ambat. After the battle, Grodek surrendered himself to EFF command for discipline. EFF, hoping to get the support from the public opinions, covered up the truth of the Diva's operation; they claimed that Diva acted independently on behalf of EFF (in fact, Diva acted independently by its own crew's wishes, not by the command of EFF) and defeated UE in Ambat. The truth about UE was revealed, but only as a nation in Mars named Vagan and EFF didn't reveal its origin to the public.
Unknown to them in Mars orbit, a Vagan battleship carrying Medel Zant launches and heads for the Earth Sphere.