The Communication Player (COMP) is a portable gaming system capable of sending and receiving emails and browsing the web. Kazuya Minegishi and his friends each receive a COMP from Kazuya's ominous hacker cousin, Naoya, who warns them that they will need the devices to survive. Confused, the three dismiss Naoya's warning and proceed to open a strange "Laplace Email" in their inboxes. The email claims that someone will be brutally murdered, followed by a massive explosion and a blackout that will take all of Tokyo offline. They assume it is a joke until the terrifying events unfold before their eyes. Shaken, the three soon discover that Naoya has loaded a demon summoning program onto their COMPs, causing powerful demons to emerge from their devices and attack them. Upon being defeated, these demons forge contracts with them and become their partners. Armed with the ability to summon demons and predict the future via email, the three friends fight to survive in their new, demon-infested reality. Along the way, they must uncover the truth behind the summoning program and what happens when they alter their fates.