In a futuristic post-war world, Tatsuki Akiyama, a bounty hunter and assassin, supports his little sister Akari in an almost lawless society. However, when Akari is abducted in the middle of the night, Tatsuki is compelled to join The Sanctum Rebellion, a former government turned resistance, in order to fight for their cause, but ultimately to rescue his sister from the clutches of the Four Remaining Governments.