Season 1

While the mechanized forces of Ingelmia begin to encroach on the Kingdom of Arandas, the 8th Independent Unit of Arandas is ordered back to their headquarters. Along the way, a civilian convoy is attacked by Ingelmian forces. Tokimune Susumu, a rookie pilot, disobeys orders and tries to rescue the civilians only to get his own Trail Krieger mech destroyed in the process.

With his Trail Krieger destroyed and no other options immediately available, Tokimune is forced to steer the Argevollen home with the rest of his unit. Jamie tags along to finish delivering the robot to her company, and reveals that the system has been slaved to Tokimune's own body signature so that only he can pilot it.

The 8th Independent Unit finally makes it back to a nearby castle before being told by their superiors they will have to move again to stop the Ingelmian advance and cover the retreat of friendly forces. Commander Samonji devises a plan to collapse the "Gates of No Retreat" by planting lots of explosives along the canyon walls, while his unit will buy time for Ardanas forces to evacuate the area.

The team reaches headquarters for some much needed rest and relaxation. While there, Tokimune is berated by his teammates for constantly disobeying orders and putting them in deadly situations. Jamie begins to show signs of PTSD while in the shower.

Jamie runs into Tokimune as he plants flowers near his sister's grave, stating that he became a Trail Krieger pilot in hopes that he would quickly rise through the ranks and find the truth behind his sister's death. Jamie composes a message to her company demanding that Tokimune be taken off the Argevollen before he gets himself and the robot killed, but can't bring herself to submit it.

Tokimune awakens to find himself sealed in the Argevollen's cockpit. As Jamie scans the readout, she realizes that the system prioritized protecting its pilot before shutting down, and only a manual reboot of Argevollen's systems will get Tokimune back into the fight, so with nothing more than a helmet and Private Koshikawa's help, she runs through the forest to reach the Argevollen.

The 8th Unit is given unofficial R&R on the neutral island of Bellhals. Jamie has a coupon to a luxurious spa on the island and plans to visit, but is called by her boss at the last minute to update Argevollen's OS. The rest of the women go to the spa, while the men hang out at a local bar.

The episode opens with a flashback of Samonji meeting Tokimune's sister in the same sunflower field sometime in the past. In the present, Samonji orders everyone back to the command post. He later receives confirmation from his friend Quasimodo that the reason his supplies were late was due to an Ingelmian sympathizer using the same ship to transfer some unnamed heavy equipment.

Richthofen stops at a bar to meet up with his friend, Major Conrad. As the two reminisce about old times, Conrad reveals that both of them have been ordered to a forward base in Zong to help lead a full-scale assault into the heart of Arandas. Meanwhile, Samonji informs the 8th Unit that they have been ordered to quickly strike the Ingelmian base at Zong to blunt the invasion before it starts.

Samonji and Suzushiro are both recalled to headquarters while the rest of the 8th Unit heads to Wishpe for some R&R, which happens to be Okui's hometown. The 8th Unit only gets a little rest before a mechanized Ingelmian party begins moving towards the town. With their normal command staff MIA and the next ranking NCO sick with food poisoning, command of the 8th Unit ends up falling to Okui.

As the 8th Unit heads back to headquarters, Brigadier General Cowen of the Arandas Army nonchalantly informs Samonji that Arandas is slowly losing the war, Tokimune is the younger brother of his late subordinate Reika, and that the Argevollen was originally meant for his own use.

Suzushiro tells Tokimune about the events behind his sister's death at Argent Point. At the time, Samonji was a Second Lieutenant and the leader of the base's security force which included herself and Quasimodo. Reika was a Sub-Lieutenant and the pilot for a new Trail Krieger that could use its pilot's brain to control unmanned mechs in the field.

Private Namie Portman arrives at the outpost where Independent Unit 8 is doing training exercises. Along with her arrival come multiple Trail Kriegers of a new model known as the ZTK5 Seiran, for which she provided testing data during production.

Several remote Arandas Army bases have been completely wiped out by what Suzushiro refers to as a ghost, as there were no witnesses left alive to detail the new threat. Independent Unit 8 has been ordered to the base at Kitazamahara to help defend the base from this new threat. Elsewhere, the schism between the Ingelmian Army officers and the Intelligence Division widens as both sides are racing to acquire newer Trail Krieger models.

The Kitazamahara base is wiped out in the battle between the Argevollen and the new enemy unit. The 8th retreats to Pudder base to recover and regroup. They chart a course through an abandoned industrial city, and bait the "Ghost" into attacking, but in the ensuing battle Tokimune loses control.

Samonji forbids Tokimune from piloting the Argevollen. Tokimune listens to a recording of himself going out of control and attacking his own allies, and Samonji tells him a shocking truth: the Argevollen is based off the unit that killed his sister.

The 8th Unit withdraws from the Pudder supply base as a huge legion advances. Samonji refuses to allow the Argevollen to launch, despite the fact that they're outnumbered, but Cayenne puts pressure on him. And when the Sturm Alpha shows up, he no longer has a choice.

The 8th Unit successfuly retreats after a fierce battle with the Sturm Alpha. But Tokimune collapses after leaving the Argevollen, and is in a coma. Jamie blames herself for not being able to stop him, and Samonji says that he's been defeated.

Arandas and Ingelmia both want to make peace to end the stalemate. Samonji is brought out by Cayenne, who tells him that if the war ends like this, all the sacrifices will have been for nothing. Cayenne shows him a line of Perfevollens, mass-produced Argevollen units, and asks him to make a choice

The Perphevollens have been put into combat. Samonji has left the 8th Unit to lead them. They're pushing back the Ingelmia army and winning many battles. Meanwhile, the 8th enjoys a short break at a northwestern supply base, but the troops are uneasy...

Ingelmia has introduced the Sturm Beta to counter the Perphevollens. The tide of battle turns towards Ingelmia's side again. General Cayenne, disgusted with the other generals desire for an easy peace, rebels against the Arandas government, with Samonji at his side.

Cayenne rebels against the Arandas military, and Captain Samonji sides with him. The 8th Unit goes to stop Samonji, but Argevollen is captured instead.

By deliberately leaking information, Cayenne is able to capture the enemy Sturm Betas. The U-Link squad is now much more powerful, and Samonji has broken through the Gate of No Retreat. Jamie and Tokimune swear they will get Argevollen back.

Tokimune Susumu faces Ukyo Samonji only to be forced out of the ARGEVOLLEN. Samonji walks off in his the PERFEVOLLEN Command unit with all other Kriegers. He contemplates what it is he's been doing.