The Isolated Zone: Shinku Chitai

“Z,” a biological weapon developed in the utmost secrecy, spread following a major earthquake that devastated the Kantō region. To contain the epidemic, the Japanese government decided to isolate the area, abandoning the survivors to their fate, now prisoners of a hostile world.
Tetsu was 12 years old when the disaster struck. A year later, he became the leader of a group of child survivors threatened by ruthless gangs working for a man calling himself the Emperor.
Determined to uncover the truth and find those responsible for this tragedy, Tetsu decides to embark on a grand project to conquer territory. His goal: to escape from Kantō.

(Source: Nouvelle Hydre, translated)