You're not alone. On any day, anywhere.
Yūta Hibiki, who is a first-year high school student living in Tsutsujidai, one day wakes up to find he has lost his memories. And he meets the "Hyper Agent Gridman" on his old computer
Gridman says that Yūta has a mission he must fulfill, and Yūta sets out to find the meaning to those words and his memory loss.
Yūta's friends - Shō Utsumi, Rikka Takarada, and Akane Shinjō - would always help him and spend their days with him. But, their tranquil days are suddenly and easily crushed with the appearance of kaijū.