The Universal Century began with mankind moving its burgeoning population into outer space. The cluster of colonies furthest from the Earth, Side 3, proclaimed themselves the Principality of Zeon and launched a war of independence against the Earth Federation. Now, it is nearly one year since the war broke out - Universal Century 0079. Federation troops and Zeon forces carry out a fierce battle in the "Thunderbolt Sector" in 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. Mobile Suit pilot Io Flemming is among the Federation soldiers who are dispatched to the area, where Zeon sniper Daryl Lorenz awaits them on the battlefield.