The story is set in 2007, when Professor Takuma Nekasa uncovers a gene code that will unlock the human body's greatest mystery and expose mankind to its greatest threat. As a result, Gawl, Koji, and Ryo—three young scientists from a future period—have traveled back in time to undo this mistake. Though the trio intended to arrive one year before the calamity, they are instead transported three months prior to the event. In their effort to save the world, they are opposed by the mysterious and cunning Ryuko Saito, a scientist who prefers the future as it is. Saito is assisted by Generators, unearthly assassins posing as humans. As Ryo and Koji try to complete their mission, Gawl himself must "generate"—becoming like his enemies to fight on their terms.