
In "SSSS.GRIDMAN Grand Episode," Yuuta Hibiki finds himself waking up in a strange room belonging to Rikka Takarada, only to realize he has lost all his memories. To his astonishment, he hears a mysterious voice calling his name from a nearby room. Upon investigating further, Yuuta discovers an old computer shielding a giant robot known as Hyper Agent Gridman, who introduces himself and intrigues Yuuta with his powerful presence.
As Yuuta tries to make sense of his missing memories and the presence of Gridman, he notices something peculiar: Rikka is completely unaware of Gridman’s existence, nor can she perceive the menacing monsters lurking outside in the thick fog that suddenly envelops the city. Things escalate quickly when a colossal monster appears and begins to wreak destruction across the town. Amid the chaos, Yuuta instinctively merges with Gridman via the computer, finding himself propelled into the heart of the battle as they confront the gigantic threat.
Joining forces with Rikka and their pragmatic classmate Shou Utsumi, Yuuta forms the "Gridman Alliance," a team dedicated to defending their city from the rampaging monsters. Together, they face relentless challenges as they strive not only to defeat these terrifying creatures but also to uncover the truth behind their mysterious origins. With shifting alliances and secret motives, the members of the Gridman Alliance must navigate a complex web of danger and discovery in their quest to protect their home.