Adapted from the manga of the same name by Haruchika Negi, the story unfolds 13 years ago when a horde of monsters invaded Earth. The monsters clashed head-on with the Dragon Guardians, an organization tasked with protecting the planet. Although they engaged in battles almost every week, the truth beneath the surface differed from what met the eye. In reality, the monsters were defeated within a year, yet the Guardians forced them into staged battles in front of many citizens who idolized the Dragon Squad. Fed up with the humiliation, the monsters decided to instigate change by infiltrating the squad and defeating them from within.