Katana zero takes place in the dystopic, neo-noir metropolis of New Mecca. The games plot is heavily affected by an invasion of an unnamed Asiatic nation, referred to as the "Cromag War," launched by either New Mecca or whatever controlling government rules it. New Mecca's faction is implied to have lost the ensuing conflict. The player controls a katana-wielding assassin called Subject Zero, nicknamed "The Dragon", as he completes various assassinations given to him by his psychiatrist, who also supplies him with 'Chronos', a drug that allows him to slow down time and predict the future.