The following morning Alcor surprises Hibiki, Daichi and Io by making breakfast for them, while Io withholds her fate from Hibiki and Daichi. Later, Alcor visits Yamato and expresses his concern over what consequences Io's death would have on Hibiki, although Yamato shows no sympathy for Alcor's anguish. Finally, Io is summoned by the JP's while Hibiki and co. are briefed on the Septentrione: Mizar's abilities of self-replication. As the group expresses concern on a battle plan, Yamato and Makoto reveal to their horror, Io inside a machine connected to the "Brionac" and their plan involving Io's sacrifice for Lugh. Furious, Hibiki demands another plan, although Yamato's logic trumps him. Finally Mizar manifests in Tokyo prompting Yamato to begin the summoning for Lugh. Simultaneously, Hibiki, Daichi and Hinako receive Io's death clip, causing Hibiki to storm out of the JP's headquarters.
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.
