The countdown to extinction begins on Sunday with the arrival of the Septentriones, otherworldly invaders set on the eradication of mankind. Caught in the crossfire, Hibiki Kuze and his friends join in the war for humanity's survival by signing contracts with demons to become "Devil Summoners." Soon, their abilities attract the attention of JP's, an underground agency led by Yamato Houtsuin. Once recruited into JP's, Hibiki and his friends fight and bond alongside other ordinary citizens who are Devil Summoners.

However, with each new day, another Septentrione appears to wreak havoc upon Japan. Even if many lives are lost in the process, before that night ends, the young summoners must defeat the invaders at all costs.