Gato flies back to the Garden of Thorns, a secret Zeon colony base in the Shoal Zone, to present the GP02 to Delaz. However, a chance encounter with Zeon commander Cima Garahau rankles him when their ships almost collide. Upon delivering the GP02, Delaz makes an Earth Sphere-wide declaration of war, explaining that the GP02 and its nuclear weapon is proof of the Earth Federation's military buildup. Meanwhile, aboard the Albion, Nina tries to get closer to a dense Kou when the alert sounds. Kou and the rest of the Albion's mobile suit pilots engage the Zeon intruders. However, Nina's warning about the GP-01's poor mobility in space without the so-called Full Vernian (Full Burnern) backpack proves true as Kou crashlands in the Albion under heavy damage.

Cima's blackmailing apparently works, as Anaheim asks Nina to be reassigned away from the Albion and out of the mobile suit development team altogether. Keith, who dates Mora, offers Kou movie tickets so he can ask Nina out after a field test. He does make a move, but a remark about the tests angers Nina again. Meanwhile, Kelley gets paid in gold bullion for his work on the Val Walo, but is shocked to hear that the Zeon forces do not want him piloting it for the new campaign. Incensed, Kelley takes out the mobile armor and challenges Kou to fight him so he could prove himself worthy of joining the Delaz Fleet again. When Nina gets in the way, Kou finally admits his feelings for her and defeats Kelley, who does not bail out from the exploding Val Walo because he never installed an escape system.

Gato retreats after the nuclear strike destroys two-thirds of the Federation's fleet, but runs into Kou. As Nina breaks down watching them fight, both of their mobile suits take heavy damage and the pilots flee before they explode. Meanwhile, Cima's fleet hijacks two colonies in transport and later blow off one mirror each from them. When the Albion crew is informed of the colonyjack, Nina correctly theorizes that the colonies will crash into each other, with one in direct course for the Moon. She also reveals the existence of a third Gundam built under the GDP.

The battle to stop the colony goes full-blast, with the Federation and Cima's forces working together to protect the Solar System II on one hand and the Delaz fleet shepherding the colony on the other while the Axis Advance Fleet stands back. Kou kills Cima in the fracas. The Solar System II fires, but Gato destroys the command ship, resulting in a weaker blast that barely damages the colony. As it breaks through the solar array, Gato enters the colony and inputs the final course corrections. Kou tries to stop him, but Nina interferes and protects Gato as they leave, revealing that they were once lovers. The two pilots continue to fight after Gato has Karius bring Nina to safety. The Solar System II remnants fire again, with many forces on both sides destroyed as the colony crashes into the Midwest. The Federation orders the Axis Advance Fleet to leave the Earth Sphere immediately, having overstayed their welcome, but Gato leads the Delaz Fleet survivors to attempt a breakthrough and dies in a kamikaze attack on a Federation ship. Several weeks later, Hymen and Bask Om announce the creation of the Titans. All records of Operation Stardust and the GP are erased, including Kou's one-year hard labor sentence. He eventually reunites with Nina, Keith, and Mora.