Yuuta Hibiki is a first-year high school student in Tsutsujidai. One day, he wakes up with amnesia. He then sees the show Hyper Agent Gridman on an old laptop. After hearing Gridman’s speech about fulfilling a mission, Yuuta decides to start looking for both the meaning of those words and his memories. While being completely unaware of how things would work normally, he goes on with his daily life helped out by his new classmates Shou Utsumi, Rikka Takarada, and Akane Shinjou.

But, those peaceful days were easily destroyed by the appearance of giant monsters...