It is the latter half of Universal Century 0096 and the Earth Federation government feel threatened by the existence of the "Psycho Frame." First lieutenant Mehmet Merka, a member of the intelligence bureau under their jurisdiction, forms a special force called "Mastima" and is given an important mission to infiltrate and investigate the severed "Axis," an asteroid that drifts near the Earth Sphere. There are two civilians by the name of Arlette Almage and Danton Hyleg, both of whom were once an engineer and test pilot respectively for the Principality of Zeon and Neo Zeon, who accompany Mehmet as members of the investigation team. When the investigation team infiltrate Axis, they are assaulted by the private army "Birnam's" Newtype Gundam despite the base being thought to be abandoned. Although they fight back with the red "Zaku III Custom," a mobile suit that Danton and Arlette were both once involved with, they confront various critical situations.
Amidst all this, Arlette keeps certain "feelings" hidden away in her heart and is faced with the wreckage of the Sazabi that was left behind on the surface of Axis...

Source: gundam.info

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Prequel: Kidou Senshi Gundam Unicorn
Full story: Mobile Suit Gundam: Twilight Axis - Akaki Zan'ei
Sequel: Kidou Senshi Gundam Narrative