One day, Shirayanagi Kei, a high school student who loves games and candy, is dragged into a battlefield by a mysterious woman who calls herself Meiyin. Meiyin tells the gathered people, "You no longer have a household registration." "Please become an experimental observer." Everyone present is given special abilities to participate in various projects. Kei, who is determined to destroy this organization, uses abilities that no one can predict and rare "brain" abilities as weapons, and a new era of brain-based ability battles begins.