Yuuta Hibiki is an amnesiac first-year high school student living in the fictional Tsutsuji-dai, based on Suginami Ward. He encounters the voice of the robot Hyper Agent Gridman in an old computer, who tells that the boy has a mission he must fulfill. Yūta sets out to find the meaning to those words and his memory loss. The sudden appearance of destructive kaiju eventually changes the usual dynamics of Yuuta and his classmates. Yūta is able to merge with Gridman to fight these kaiju, but after each attack, the memories of regular residents are reset and those who die are forgotten.