The First Battle refers to the battle that happened during Aoba's first arrival in 2088.
To change the tide of the war, the Free Pact Alliance military had decided to use the Coupling System, which was prohibited by the council due to bad prior results, and constructed two coupling Valiancers as well as a ship, the Cygnus. It was a secret project yet Zogilia was able to learn about it and attacked to capture the new Valiancers, presumably at the request of Wilhelm Hahn. They sent Alfred Gallant's Valiancer unit to secure and steal the two new Coupling Alliance Valiancers.
While Lee Conrad, Jarl Duran and Dio Weinberg were able to reach their valiancers, Marcus was killed by falling debris before he boarded Luxon. Dio lost his coupling buddy but was not overly moved by it. They stayed in the hangar for a time. Lee asked for Bradyon to be removed from the battlefield as it had lost its chance to couple, and was being dealt with the threat of being captured.. It was authorized by Gengo Kuramitsu who was in the Cygnus, still underground.
Suddenly, Aoba teleported awakened into Luxon's cockpit and the coupling system announced he was compatible with Dio, as this happend, Dio and the Cygnus crew noticed he was there. Aoba wondered where Hina was. Lene Kleinbeck opened a communication but she was annoyed when it was revealed that Aoba was a civilian, thus had no idea how to pilot or even get out of the valiancer. He was told to stay there.
However, captain Kuramitsu, seeing how Bradyon was in trouble and Luxon defenseless decided to allow the Valiancers to couple despite not knowing one of the pilots at the time. As Aoba recognized Dio's name, though he did not know him. They were able to couple, just as an enemy, Mihailov, had spotted Luxon standing in the hangar and sent missiles at it. However, the Coupling was successful and as the smoke that was deployed from the missles covered his Valiancers screen cleared up, Luxon appeared from the coverage and kicked him away. Dio had Bradyon land back to back with Luxon in Coupling mode.
Bradyon flew to fight Bizon and Lasha who were surprised by its speed and strength. The Cygnus crew were happy it succeeded but Elvira and Mayuka noticed something was strange with Aoba though it did not stop the coupling. Dio mused over the fact Aoba was so compatible with him even without training.
Aoba was attacked by Mihailov but he saw Dio's hands and feet moving and imitated them which permitted him to use Luxon's sword to block the attack. However the enemy was able to push Luxon through the hangar and Aoba was violently pushed against his seat, which caused pain to him, but also to Dio, still busy fighting Bizon and Lasha, distracting him briefly and caused him to falter.
Annoyed, Aoba kicked Mihailov away and flew away much to his shock. Mihailov pursued him and Aoba had another flash which permitted him to fly, counter attack, defeat and kill his attacker, much to Lasha and Dio's surprise.
Having seen the new Valiancers, Bizon decided to order the troops to retreat. Zogilian forces and Alfred's Valiancer squad thus retreated from the area.
After watching Luxon, Dio initiated decoupling, taking Aoba by surprise and he dropped out of the sky. Luxon was surrounded by Beryl Assault, Beryl Commander and Bradyon. Elvira came to see the pilots with Mayuka, joining Lee and Dio that had come out of their Valiancers, looking up at Luxon. Lee commented Aoba probably had no idea of how to get out, which was entirely true. He eventually got out. Aoba was taken in custody by the Alliance. He told them he was a time traveler though they did not believed him, the Cygnus crew did not saw him as a threat. They decided to keep him on board because he had seen the Alliance's secret project. Elvira revealed Aoba's belonging were all dating from 70 years but still would not believe what he had said. She admitted he could have found a better story. Though he was not really considered to be a threat.
Kuramitsu had Luxon modified with new specs; to suit Aoba's Coupling needs more, because he knew they would need him to pilot it again, for future battles.