19 months after the events at Saazbaum's Landing Castle, a UFE raiding party finds themselves shot down by the Tharsis, piloted by Slaine himself. Slaine has become a Vers Knight with the power of Aldnoah under Saazbaum, and the Vers Empire has been slowly conquering North and South America under the new support of Princess Asseylum as they plan to expand their reach. On Earth, the crew of the Deucalion prepare to finish their R&R when they come under attack from a Martian Kataphract called the Frozen Elysium, capable of freezing all matter around it by a kilometer. The UFE Kataphracts find that they can't hit this new threat before getting frozen to death, when Inaho appears in his restored training mech, using airburst grenades to create a small path through the freezing field and destroy the enemy. The episode flashes back to the moments after Asseylum and Inaho were shot in the Landing Castle. Slaine decided to spare Saazbaum and escape with him and Asseylum in the Tharsis, while Inko and Yuki tried to get a wounded Inaho back to base where he needed surgery. Things looked grim with Asseylum absent and the Deucalion still unpowered, but Inaho somehow maintained enough consciousness to power the ship's Aldnoah Drive himself with powers he inadvertently got from Asseylum while administering CPR. In the present, the Princess Asseylum giving the war speeches to the Vers Empire turns out to be another Princess named Lemrina, using her guise under Saazbaum's supervision. As the night ends, Slaine goes to visit the real Asseylum, being kept alive in a medical tank.

The UFE forces gather in Earth's orbit at Trident Base, built into an asteroid, as they prepare for a large-scale operation against another asteroid base called Marineros owned by Vers. Meanwhile, Saazbaum rallies his own forces for a quick strike on Trident as they travel to Marineros Base. Slaine finds that Lemrina shut down the Tharsis' Aldnoah Drive, and tries to reason with her to get it running again. Eventually, Slaine gets her to restart the Tharsis. As Lemrina visits her still-unconscious sister and schemes to replace her position, the Martian forces begin their assault while the UFE dig in on nearby asteroids. Inaho makes use of his new cybernetic eye to accurately shoot down several enemies, but Slaine somehow manages to see the trajectories of the shells being fired at him in the Tharsis, and dodges at the last second. The Martian forces soon pass by the base as Inaho and Slaine confirm that they fought each other.

Both UFE and Vers forces prepare for battle on their respective asteroid bases. Magbaredge confirms with Inaho that it wasn't Asseylum's blood alone that gave him Aldnoah activation, but something that was transferred when he gave her CPR. Meanwhile, other Counts of the Vers Empire show open contempt at Slaine for being a Terran, but before they harm him, Saazbaum abruptly announces that he is adopting Slaine as his son and legal heir. Finally, Trident and Marineros bases are close enough that the two sides begin their attacks. Inaho shoots down several enemy spacecraft and eventually runs into Slaine again, confirming that he is somehow able to accurately predict the near future like himself. Saazbaum appears in his refurbished Dioskuria II, and mentions that his shield's weak spot is different from last time as he chases down Inaho. With Inaho's help, Inko manages to disable the Disokuria II's shield just as a micrometeoroid shower hits it, disabling the Kataphract. Slaine then tells Saazbaum that the shower was actually his own work, using Tharsis' systems to accurately pinpoint where Saazbaum would be two minutes in the future so he could destroy him as revenge for shooting Asseylum. After a second micrometeorite shower finishes off Sauzbaum, Slaine becomes a Count of the Vers Empire while Inaho confirms from Slaine's speech that Asseylum is alive.

As Slaine ascends the ranks, he puts a plan into motion to deflect scrutiny. Meanwhile, Yuki prepares for a possible reunion with Inaho as the Terrans face another Kataphrakt threat.

The Earth forces now have Count Mazuurek as a captive. With such a high value prisoner, what will this mean for the relations between the Earth and Mars? And with the Deucalion back on Earth, what is the next move?

On Earth, the UFE launches an attack on a Martian Knight whose Kataphract can fire powerful lasers, preventing UFE forces from being able to get close. While UFE forces distract the Vers Kataphract, Inaho begins directing artillery fire from the Deucalion main cannons. Because Deucalion uses traditional artillery shells, it can arc its shells over the curvature of the Earth, protecting it from reprisal attacks since lasers can only travel in a straight line. Eventually, the Deucalion manages to score a direct hit on the Vers Kataphract and destroy it. Inko then confronts Inaho about him freeing Mazuurek, and Inaho acknowledges what he did, and that he didn't want Inko to get involved. At the Moon base, Slaine and Count Marylcian begin their duel. Marylcian's Herschel uses numerous unmanned drones to attack Slaine, straining the Tharsis' abilities to the limit. However, Slaine manages to outsmart Marylcian by luring him into a tunnel, allowing him to destroy all of the Herschel's drones. The now vulnerable Marylcian is then killed by Slaine, who seizes all of Marylcian's assets. Lemrina, still posing as Asseylum, makes an announcement to the rest of the Martian Knights, declaring that they form their own kingdom independent from Vers, and that she and Slaine will be married. Afterwards, she visits the still comatose Asseylum and considers shutting down her life support, but decides to spare her life. However, after Lemrina leaves, Asseylum begins to regain consciousness.

Princess Asseylum's marriage to Slaine is officially announced. Meanwhile, Slaine organizes an unprecedented attack on Earth after rallying as many Counts to his cause as possible.

The Earth Forces are on the retreat after the Vers three-pronged attack. Meanwhile the relationship between Slaine and Lemrina grows in tense.

At a loss on how to deal with a multiple Kataphraktoi attack, the Terran forces rest their hopes on Inaho's abilities. However, they may be relying on him too much. Lemrina, meanwhile, makes a move after figuring out her sister has awoken.

The Terran forces prepare a two-pronged attack on the Martians. Inaho continues to feel the negative effects of relying on his cybernetic eye. Klancain meets with Slaine.

Both the Terrans and the Martians prepare for a massive final battle. Meanwhile, with her allies dwindling, Princess Asseylum makes a valiant last-ditch effort to end the war once and for all.

Empress Asseylum declares a cease-fire and, with Slaine's resolve seemingly shaken, a rift surfaces between the Orbital Knights. Inaho and Slaine finally settle their differences on the battlefield.