In the classroom after school at Metropolitan Azalea Terrace High School, Yuta Hibiki draws GRIDMAN over and over in his notebook. This world was once created and destroyed by a girl. The one who saved the boy's heart was the super agent GRIDMAN from another dimension. The girl created a monster with a mind, and Yuta and his friends. They lived in a peaceful world, but their daily lives began to collapse with a loud bang.