In the 103rd year of Meigo (2101), the war between Sankoku and Gvardea became a limited exchance of N2 weapons. These were fearsome explosive devices which were each 10 times more powerful than a nuclear bomb, minus the radiation. The reason the treaty against the use of these weapons was broken is widely debated. The Gvardeans universally blame Sankoku, while the Sankoku'ans are split on the issue. Some Sankoku'ans believe it's the Gvardeans' faults; others believe the government and/or military are to blame. The entire planet of Kaikyuu was sent reeling by the attacks.
The Sankoku'an President, Kiko Yamato, put official blame on the Army. The country split into two parts: The old and the new, so to speak. Those loyal to the President became Fuso. Those loyal to Supreme Commander Caitlin "Kit" Pendragon were part of Old Sankoku. Kit is the commanding officer of the Sankoku army and de facto leader of the old territories, and largely wants to avoid this civil war. She blames herself for not being able to prevent the nuclear exchange, believing it's her fault all those lives disappeared in a blink of an eye.
However, she can only hold up the tenative peace for so long, as resources are running dangerously low...
The Sankoku Army has holed up in an underground base constructed from a geo-front, due to the destruction wrought upon the surface. The Supreme Commander's two bodyguards, Mia and Renji, are largely in charge of the base because the Supreme Commander's suffered a "heroic BSOD".