Mankind migrated to space colonies several centuries ago, with wars on Earth having long ended. Suddenly during the Advanced Generation (AG) Year 101 an Unknown Enemy (UE) appears and starts to attack Earth and its colonies starting a full-scale war. They destroy the space colony "Angel" in a disaster later referred to as "The Day the Angel Fell". In AG 108 the UE attack a once peaceful colony known as "Orvan". Flit Asuno, a seven-year-old boy at the time, had his mother killed in this attack. Before she died, she gave him the Asuno family heirloom—the "AGE Device" memory unit. Using plans hidden within this unit, Flit begins to develop the mobile suit "Gundam", humanity's last hope.

In the year AG 115 Flit Asuno, now age fourteen, lives on the colony "Nora" in an Earth Federation military base named "Arinsuton". After seven years of research and development collaborating with the Earth Federation, Flit completes development of the Gundam AGE-1, allowing it to self-evolve through combat experience. The UE finally begins an attack on the colony "Nora" and now Flit has no choice but to fight with the Gundam!