Yuta Hibiki wakes up in the home of his classmate, Rikka Takarada, with amnesia. A voice from an old computer, identifying himself as "Gridman," has a mission for him, but can he even survive the next day of school without his memories?

Yuta and his friends attempt to unravel the mystery of the city and everyone else's memories. However, more questions arise when a strange samurai arrives and tries to tamper with Gridman.

When the Tsutsujidai High School Festival is threatened, the Gridman Alliance must decide how to proceed. Some of them wonder if fighting is the only choice they have.

It all comes down to the line as the Gridman Alliance attempts to save Akane, but do they have what it takes to battle the monster within?