A mundane Monday morning turns into a nightmare when a cryptic television broadcast announces: "They have arrived." Mysterious wealthy elites begin purchasing citizens' homes, including Litus’s, just as colossal beasts appear and start devouring everyone in sight.

Three years later, humanity is at war. Conventional weapons have failed, and only a select few are chosen for elite combat units. Litus enters the entrance exam, using the memories of "Tusa’s" fighting style to pass the theoretical phase. During the practical test, a mysterious boy reveals a chilling truth: there is a dark secret behind the appearance of these monsters.

Despite his efforts, Litus is assigned to the "Cadaver Disposal Unit" alongside the same mysterious boy. It is there that he is handed a book with a mountain on the cover—the key to uncovering the truth about this broken world.