Yuta Hibiki (Gridman): The protagonist of SSSS.GRIDMAN who transforms into Gridman. He has a natural, easygoing personality and is fundamentally broad-minded, gentle, and kind-hearted, often trying to cover for Gridman's mistakes. However, he also possesses a brave side, facing off against Kaiju without hesitation. He has feelings for Rikka. Member of the Gridman Alliance (Ally).

Rikka Takarada: One of Yuta Hibiki's classmates. Her family runs the thrift shop "Junk Shop Aya." While she is a modern high school girl, she carries a slightly cool aura and is characterized by a somewhat listless tone of voice. She struggles with gauging the right distance from others, often interacting from a step back or spending her private time alone, showing a tendency to be somewhat socially awkward. Member of the Gridman Alliance (Ally).

Sho Utsumi: A boy with glasses and a classmate of Yuta Hibiki. Having become friends with Yuta three months prior in the spring, he is a good-natured person who treats the amnesiac Yuta the same as before. While he usually has a calm demeanor, he is actually quite hot-blooded and full of curiosity. When Ghoulghilas appeared, he went to watch despite the danger, and when Yuta transformed into Gridman, he took the lead in finding ways to provide support, cheering with a bright expression when the tide of battle turned. He has a spirited side, even suggesting the formation of the "Gridman Alliance" after the battle. Member of the Gridman Alliance (Ally).

Akane Shinjo: Yuta Hibiki's classmate who sits at the very back by the window. She is the class idol, but her other face is that of a Kaiju figure sculptor and the "mastermind behind the Kaiju incidents." To vent stress from trivial matters (things even Takeshi might endure), she creates Kaiju figures which her partner, Alexis Kerib, materializes in Tsutsujidai to go on a rampage. She watches the destruction via drones on her dedicated tablet. Antagonist.