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 is distressed that so many boys have lost their lives because of her. Mikazuki takes her to the farm run by Biscuit's grandmother, where an unexpected encounter awaits.

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.

The members of Tekkadan need a guide in order to reach Earth despite Gjallarhorn's surveillance. To gain a powerful backer, they attempt to negotiate with Teiwaz, which is based in the Jupiter Sphere.

Tekkadan has made contact with Turbines, which runs Teiwaz's transport division. But they find themselves clashing with Turbines over their group's origins and property.

Having demonstrated Tekkadan's strength and legitimacy to Naze, the leader of Turbines, Orga and the others renew their negotiations with Teiwaz. Meanwhile Atra visits Turbines's warship, bringing the frustrated Kudelia with her.

Accompanied by Naze, Tekkadan visits the Saisei, the stronghold of Teiwaz, in order to meet with Teiwaz's representative McMurdo Barriston. Here, Orga receives a surprising proposal from Naze.

Tekkadan and Turbines go on ahead to Earth, leaving Mikazuki and Yukinojo on the Saisei to complete final adjustments to the Barbatos. But the events aboard the Saisei have greatly affected their respective states of mind.

While on patrol, Akihiro and Takaki encounter unknown enemies and engage them in battle. The attackers turn out to be Brewers, a pirate group that operates between Mars and Earth.

Mikazuki and Orga learn that Akihiro's long-lost younger brother is one of the Brewers mobile suit pilots. Tekkadan challenges Brewers in order to get back Akihiro's brother.

The battle with Brewers has cost many lives on both sides. The survivors hold a funeral service to pray for the rebirth of their fallen comrades.

After overcoming many difficulties, Tekkadan is finally about to reach Earth. Its members head for the Dort colony cluster, to deliver an item that Teiwaz asked them to transport when they were aboard the Saisei.

Just as on Mars, the colonies suffer great disparities with Earth, and a protest movement has begun among the increasingly dissatisfied workers. As it gradually intensifies, Tekkadan is caught up in various schemes.

The colony workers have launched a protest movement against the company that employs them. As they grow more radical, the situation finally develops to the point of a Gjallarhorn intervention. Before she knows it, Kudelia has been drawn into the heart of the uprising.

Kudelia and Tekkadan witness Gjallarhorn's brutal suppression of the workers. Seeing the true situation of the colonies, Kudelia makes a fateful decision.

Tekkadan's members attempt to leave the colonies behind and descend to Earth at last, but they miss their chance due to one last item of business in the colonies. They are contacted by someone who claims to be their supporter.

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.

As Tekkadan heads for Edmonton, it finds Carta blocking the way, seeking a showdown. However, Mikazuki and the others won't let their progress be halted, and they press on ahead.

Orga and the other Tekkadan members have finally reached Edmonton, but they are attacked by Gjallarhorn, which seeks to prevent Makanai from making it to the parliamentary session.

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.