An amnesiac, happy go lucky youth named Shoichi Tsugami uses the power of Agito to unravel his mysterious past and battle beings known as Unknowns. In response to the Unknown threat, the police unleashed their newest weapon, the G3 powersuit primarily used by Makoto Hikawa. More mysteries unfold with the appearance of Ryo Ashihara, who transforms into a pre-Agito known as Gills. He seeks the truth about his father's suicide. These mysteries and others collide, as the true nature of Agito would ultimately determine the fate of humanity.