Under Yamato's order, Hibiki, Daichi and Io rides on the secret train of JP's to Osaka to help find their chief scientist, Fumi Kanno, who has lost contact recently. They are greeted by another summoner of JP's, Hinako Kujou, at their arrival, but the other summoner Keita Wakui is less welcoming of the three fellow summoners and is returning to his mission of hunting down malignant demons. At the Osaka headquarter, its computer system is under attack from the whole Japan's network. At the same time, Hinako receives Keita's death clip, Hibiki instantly concludes that the scene of Keita's death is related to the hacker attack. Although Hibiki asks an operator to inform Keita not to head to the location of his death scene, Keita cannot receive the call due to being ambushed by Gozuki and Mezuki. All four summoners head to the abandoned theme park where the hacker attack originates from.
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.
