On Sunday, the clock starts ticking towards extinction as the Septentriones, unearthly intruders hellbent on decimating mankind, make their appearance. In the midst of this turmoil, Hibiki Kuze and his comrades enlist as "Devil Summoners" by forging deals with demons, joining the battle for humanity's survival. Their exceptional abilities attract the attention of the underground agency, JP's, led by Yamato Houtsuin. Upon joining JP's ranks, Hibiki and his companions unite with other ordinary people who have become Devil Summoners. Nonetheless, as each day passes, another Septentrione shows up to cause chaos throughout Japan. Despite the potential loss of countless lives, the youthful summoners must defeat the invaders by nightfall, no matter what the cost.