During the Earth Federation's assault on the Zeon's A Baoa Qu fortress, Io and his comrades escape captivity while several Zeon forces retreat, taking Io's Gundam with them. Eight months after the end of the One Year War, the Federation continues to battle Zeon remnants on Earth. The Federation carrier Spartan enters Earth orbit, but a Musai-class ship launches its Komusai shuttle for a kamikaze run on it. Suddenly, a new Gundam piloted by Io is launched from below and it slices the Komusai in half to save the Spartan.
Federation troops and Zeon forces carry out a fierce battle in the Thunderbolt Sector in what was once Side 4 "Mua". The Thunderbolt Sector is a shoal zone composed of the debris of destroyed space colonies, named for the electrical discharges from the metal debris. MS pilot Io Flemming is among the Federation soldiers who are dispatched to the area, where Zeon sniper Daryl Lorenz awaits them on the battlefield.
