It's the year AC (After Colony) 195. Over the past century, humanity has established a number of space colonies, giant wheel-shaped constructs that are home to millions of people. These colonies are grouped in clusters at the five Lagrange points, areas of relative stability in Earth orbit.

Heero Yuy

For decades, while the Earth's surface was wracked by war and civil strife, the peace and quiet of the space colonies presented an attractive alternative for war-weary settlers. When the terrestrial wars ended, a new world government was established, a "United Earth Sphere Alliance" committed to bringing about peace through force of arms. In the name of peace and justice, the Alliance seized control of the colonies.

To lobby the Earth's nations for autonomy, the space colonists chose a man named Heero Yuy as their representative. The charismatic Yuy united the colonies, and his message of demilitarization and non-violence was well-received by the people of Earth. But when Yuy was assassinated in the year AC 175, the colonists' hopes were crushed and the colonies thrown into turmoil.

Tyranny of the Alliance

Under the pretext of restoring order to the colonies, the Alliance staged a second military intervention, using humanoid fighting machines called mobile suits to crush all opposition. The colonies were placed under martial law, and all communication and cooperation between colonies was prohibited. Even terrestrial nations sympathetic to Heero Yuy's philosophies, like Europe's pacifist Sanc Kingdom, were crushed by the Alliance's overwhelming force.

Behind the scenes, the Alliance is being manipulated by the Romefeller Foundation, the powerful industrial combine that develops and manufactures its mobile suits. The Alliance's elite mobile suit corps, the "Specials," is trained and staffed by the Romefeller Foundation. In fact, the Specials are nothing but a front for OZ, a Romefeller subsidiary which has been recast as a secret society. Answerable only to the Romefeller Foundation, OZ has infiltrated the highest levels of the Alliance military.

Operation Meteor

After two decades of oppression, a network of rebels based in the space colonies decides to strike back at OZ and its puppet Alliance. Resistance groups at each of the five colony clusters work independently on their part of Operation Meteor, each retaining the services of one of the scientists who helped create the first mobile suits. Using the super-strong armor material Gundanium, the scientists construct advanced mobile suits called "Gundams," entrust them to five highly-trained, resourceful young pilots, and dispatch them to Earth to wage guerilla war against the Alliance.

Of the five Gundam pilots, the L5 colony cluster's Chang Wufei, L4's Quatre Raberba Winner, L3's Trowa Barton and L2's Duo Maxwell reach Earth without incident. But L1's Gundam pilot, a grim youth codenamed Heero Yuy after the martyred colonial leader, is intercepted by Specials ace pilot Zechs Merquise and forced to temporarily ditch his Gundam at sea. Staggering ashore, Heero encounters Relena Darlian, daughter of the Alliance's foreign minister. Heero promises to kill her to conceal his identity, but it soon becomes clear he can't bring himself to carry out the threat.