In the foggy Japanese city of Tsutsujidai, high schooler Yuta Hibiki wakes up with severe amnesia in the room of his classmate, Rikka Takarada. He hears a mysterious, disembodied voice calling to him from an obsolete computer in Rikka's family shop. Upon approaching the monitor, Yuta is sucked into the screen, merging with a giant digital entity known as Gridman, who proclaims a vital mission: to remember his true purpose and combat an impending, unseen threat to the city.Shortly after, reality shatters. A colossal, otherworldly monster manifests, wreaking havoc and obliterating buildings. Astonishingly, the general public suffers from a localized form of collective amnesia; whenever people are killed or property is destroyed, the city instantly resets, and the populace completely forgets the tragedy occurred. Only Yuta, Rikka, and their eccentric, tech-savvy friend Utsumi retain their memories of these catastrophic events. Empowered by Gridman, Yuta physically enters the computer to pilot the giant hero into the physical world, fighting alongside Rikka and Utsumi, who operate from a base to analyze the kaiju and coordinate tactical support.As the battles escalate, the trio discovers the horrifying truth behind the attacks. A lonely, ostracized classmate named Akane Shinjo is actually the creator of the monsters, fashioning them in secret. Akane possesses god-like power over Tsutsujidai, using these kaiju to murder anyone who mildly inconveniences or upsets her, viewing the city's inhabitants as disposable toys. She is aided by a cryptic, coat-wearing entity called Alexis Kerib, who preys on her deep-seated insecurities and encourages her destructive outbursts by converting her negative emotions into physical monsters.Motivated by a desire to save both their city and Akane herself, Yuta and his friends form the "Gridman Alliance," later joined by mysterious
transfer student Sho. They forge new mechanized support weapons that combine with Gridman to grant him incredible new forms. As the emotional and physical toll mounts, Yuta struggles with his own identity, slowly realizing he and Gridman are deeply intertwined.The climax forces a confrontation with Alexis Kerib, who betrays Akane when her compliance wanes, stabbing her and absorbing her emotional energy to transform into a monstrous final boss. In a fierce, desperate battle, Gridman—empowered by the collective willpower of Yuta and his friends—defeats Alexis, banishing the entity. With the simulation ending and the city saved, Akane confronts her inner demons and chooses to wake up to face reality in the real world. Yuta's memories are finally restored, and the teenagers part ways, forever changed by their
extraordinary summer.