22-year-old Yashiro Mai was an average office worker until the day a video game console arrived in her mailbox and she was forced into playing a game known as “Nightmare.” If you refuse to participate, those dear to you will die; if you lose battles in-game, parts of your body cease functioning as penalty.

The horror of Nightmare spreads through society in a flash. To combat it, Mai’s company creates a Nightmare Strategy Team, and she's one of the members.