In 2020, a nation confronts the widespread danger of the "Others"—enigmatic creatures that drop from the sky and consume human brains. Concurrently, psionics, a hormone granting specific individuals extrasensory powers effective against the Others, is identified within the human body. Following this discovery, the nation's founder creates the Other Suppression Force (OSF) to fight these monsters and preserve humanity. Known as the Scarlet Guardians, youths possessing psionics endure rigorous training to enlist in this unit. On a certain day, the nation organizes an induction ceremony for the outstanding recruits who have finished the arduous training to become Scarlet Guardians. Included among these young elites is Yuito Sumeragi, the resolute son of the nation's founder; when he was five years old, he was saved by a woman in the OSF. To settle this debt, he joins the organization, keen to apply his training. As he encounters his new comrades, he encounters a significant issue—the woman who rescued him years prior looks very much like one of his teammates. Yet, this ought to be his smallest concern—unaware to him, a conspiracy is developing, one capable of destabilizing the entire country.