The Federation and Neo-Zeon collaborate to capture a rogue suit.

One year has passed since the events of Mobile Suit Gundam Unicorn and the Laplace's Box was opened. Following the conflict called the "Laplace Incident", the Neo Zeon remnant force known as the Sleeves is destroyed. Both the Banshee and Unicorn Gundam are sealed away from public consciousness, locked in secrecy and meant to be forgotten by history. However, sightings of another Gundam are suddenly being reported. The Unicorn Gundam 03 Phenex, thought to be lost since two years ago, has reappeared.