In the midst of ongoing protests by citizens of the Martian colony Chryse demanding independence from the Earth government, the Chryse Guard Security is assigned to protect Princess Kudelia Aina Bernstein on her diplomatic mission. When the CGS headquarters is suddenly attacked by Gjallarhorn forces, the Third Army Division, having just been abandoned by their superiors, strike back with the ancient Gundam Barbatos, piloted by Mikazuki Augus.

The adults of CGS flee in the face of Gjallarhorn's attack, using Mikazuki and the other children as decoys. Gathering the children who have been left behind, Orga decides to fight back against Gjallarhorn, and puts a certain plan into motion.

Thanks to Mikazuki and the Gundam Barbatos, Orga's group has temporarily repulsed Gjallarhorn, though not without many sacrifices. As they are discussing their next move, one of Gjallarhorn's Graze mobile suits again appears at the CGS base.

Kudelia and Tekkadan finally leave Mars behind them and head for Earth. With a ship waiting for them, they attempt to travel by shuttle to a low-orbital station, but are attacked by Coral's Gjallarhorn forces.

Following a resupply by the Montag Company, Tekkadan prepare their descent to Earth, with a Gjallarhorn fleet standing in their way.

Tekkadan has finally made it to Earth, successfully introducing Kudelia to Arbrau's representative, Togonosuke Makanai. However, they will have to accompany Makanai to a parliamentary general session taking place in Edmonton.

During preparations to depart for Edmonton, Tekkadan finds itself under attack by Gjallarhorn. Setting a trap for their relentless pursuers, Orga makes a counterattack.

Though Tekkadan is exhausted by its repeated battles with Gjallarhorn, its members are still determined to get to Edmonton, and they hasten toward their goal.

In the midst of the battle in Edmonton, McGillis reveals his true motives to Gaelio while Kudelia and Makanai make it to the parliament assembly in time. As Mikazuki and Ein engage in a bloody duel, Kudelia takes her stand to give one more speech to the world while Orga gives his comrades the order not to die on the battlefield.