Gihren’s Greed: The Menace of Axis was released for the PSP in 2008. An updated version, Menace of Axis V, featuring new characters, Mobile Suits, and the Tem Ray Army campaign, came out one year later in 2009 for both PSP and PS2.
The following playthroughs are of the PS2 version of the game. I recommend starting with the Zeon playthrough for now if you are new to the game, as the Federation one is not as thorough.
Federation Campaign
In the Federation campaign, you play as General Revil of the Federation Forces and attempt to turn the tide of the One Year War against the Principality of Zeon. Events continue through U.C. 0093
Zeon Campaign
Change history as Gihren Zabi and lead the Principality of Zeon to victory in the One Year war and beyond.
AEUG Campaign
The AEUG campaign begins with the events of the Gryps conflict as you assume the role of Blex Forer and attempt to defeat the Titans.
Axis Campaign
Axis, led by Haman Karn, returns to the Earth Sphere during the height of the war between the Titans and AEUG.
Garma’s Reborn Zeon
Garma Zabi attempts to take responsibility for his family’s actions and lead the people of Zeon to a brighter future.
Casval’s Neo Zeon
Char Aznable rebels against the Principality of Zeon, reclaiming his birth name and fighting for his father’s ideals.