Ace Combat Zero

The Principality of Belka has launched an invasion on the neighbouring country of Ustio in an attempt to seize the newly discovered resources. This soon leads to The Belkan War, between Belka and the coalition forces of Osea, Sapin, Yuktobania, and Ustio itself. Ustio, having only recently seceded from Belka, loses most of its territory. As a last hope, the Ustians hire mercenary pilots to fight in their air force. Two of these mercenaries are callsigned Cipher and his wingman, Solo Wing Pixy.

Cipher and Pixy succeed in driving the Belkans from Ustio and the other coalition forces. However, when the coalition forces begin to push into Belka, Pixy starts to question the validity of the invasion. This uncertainty comes to a head when Belka resorts to nuclear weapons to fend off the coalition forces. In the confusion of the nuclear blasts, Pixy commits an act of treachery by firing upon Cipher's aircraft. Pixy then flees, and Cipher is ordered to pull back into friendly territory.

A short time after, the Belkans and the coalition forces sign a treaty for a ceasefire. However, a coalition of disillusioned pilots from Osea, Sapin, Ustio and Belka do not support the treaty; they form a terrorist organization called 'A World With No Boundaries', that seeks to erase the concept of borders between countries and create a unified world. The rest of the game is spent fighting these terrorists.

The final battle in the game is fought over The Avalon Dam in Belka, where Cipher and his replacement pilot PJ are sent to destroy an enemy base capable of launching intercontinental ballistic missiles. During the battle, PJ is shot down by Pixy, who has joined the terrorist organisation, and challenges Cipher to a battle. In the end, Cipher receives victory after shooting down his former wingman.