Devil Survivor 2 begins with the protagonist and his friend, Daichi, returning from a mock exam, along with their friend Io. The three of them receive an email on their cellphones from Nicaea, a website that forewarns its users of disasters, or their own death. The email contains a video showing them dying from a freak subway accident. Immediately after, the scene is enacted, but the students survived after being contacted by an avatar from Nicaea. As soon as they enabled the applications on their cellphone, more demons appeared, apparently wanting to kill them. The Protagonist, along with Daichi and Io, defeat the demons and become Devil Messengers, allowing them to summon demons to use to fight along them after fulfilling a contract with the Devil.
After escaping the subway, they discover that Japan was being invaded by a group of creatures called the Septentrion, their collective being named after the stars in the Big Dipper constellation. The Septentrion are able to summon the demons and wreck havoc to cities in Japan such as Roppongi and Shibuya. With their ability to summon demons, the protagonist and his friends fight off against the invaders, and joins other citizens with the same ability as they seek to end the invasion in 7 days.