The year is UC 0087. It has been 7 years since the end of the One Year War. Since the end of the war, a movement was forming within the Federation. After Operation Stardust in 0083, the Titans were officially formed. A group of Federation elites to eliminate Zeon remnants. Four years later, the AEUG begins the GRYPS Conflict with the Titans.

You, a member of either the Federation or Titans, are forced to sortie in the fourth Gundam MK-II as the AEUG attacks Green Noa 1 in an attempt to steal the Gundam MK-II. Stop the AEUG, defect to the AEUG, die fighting... That's your decision.

(I was surprised there wasn't a bot about the beginning of Zeta.)