"Can you become my teacher?"

After the case occurred in 2116 in the Southeast Asian Union, the SEAUn, Kougami Shinya kept on wandering.
In a small country in South Asia, Kougami rescues a bus carrying refugees that was being attacked by armed guerrillas.
Among them, there is a girl named Tenzing.
Tenzing begs Kougami to teach her how to fight to take a revenge.
What is the aspect of this world that a girl who seeks for revenge and a man who could accomplish his revenge can see at the margin of a world without a way out…?