Michael Owen O'Brien is an American priest serving a parish in near-future Tokyo, a city marked by societal collapse and gang dominance. He works alongside Japanese nun Sister Saeko in their religious duties. Both conceal extensive combat backgrounds as former mercenaries, possessing advanced weaponry and tactical expertise. When Takateru Suga forms a resistance to infiltrate the Koryukai crime syndicate and rescue his kidnapped sister, Owen and Saeko join the mission. Their skills prove critical during the violent assault on the Koryukai compound. Owen specifically contributes to the group's efforts to overthrow the syndicate's control over the city streets.