The Communication Player (COMP) is a portable gaming system that can send and receive emails and surf the web. Kazuya Minegishi and his friends are each given a COMP by Kazuya's ominous hacker cousin, Naoya, who tells them they will need the devices to survive. Confused, the three think nothing of Naoya's warning and proceed to open up a strange "Laplace Email" in their inboxes. The email claims that someone will be brutally murdered, followed by a large explosion and a blackout that will take the entirety of Tokyo offline. They believe it to be a joke until the terrifying events unfold in front of their eyes.

Shaken, the three soon learn that Naoya has loaded a demon summoning program onto their COMPs, which causes powerful demons to crawl out of their devices and attack them. When defeated, the same 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 change their fates.