Daisaku Kusama, also known by his International Police Organization code number U7, is the central protagonist of his narrative and the young commander of the most powerful robot on Earth. As a boy who lost his parents at a very young age, his life was defined by tragedy and an immense, early burden. His mother died not long after his birth, and his father, the brilliant scientist Dr. Kusama, was killed by the criminal syndicate Big Fire when Daisaku was only six years old. The elder Kusama had been forced to build the colossal Giant Robo for Big Fire, but in his final act, he gave his son a special wristwatch containing a radio transmitter, programming the mighty robot to respond only to Daisaku's voice. With this inheritance, the young boy gained the world's ultimate weapon and a mission to fulfill his father's dying wish: to use the robot to fight against the evil organization that sought to conquer the world.

By the age of twelve, Daisaku had become a full-fledged member of the International Police Organization’s elite team, the Experts of Justice. Despite his youth, he fights alongside seasoned adult agents against the constant menace of Big Fire. While he possesses no superhuman abilities, advanced combat training, or special powers, his courage and determination are his greatest strengths. His personality is a complex mix of childish wonder and forced maturity. Having had his childhood shattered by the death of his parents, he strives to be serious and professional like his adult colleagues, but he cannot completely suppress his natural youthful optimism and idealism. This idealism is particularly strong in his fervent support for the Shizuma Drive, a revolutionary clean energy source he initially believes can be humanity's salvation, a hope that is later challenged by the revelation of the technology’s dark and tragic origins.

Daisaku’s primary motivation is to honor his father’s legacy by fighting against evil and protecting the world. He looks up to the other Experts of Justice as his guides and surrogate family, having lost his own. Among them, the agent Ginrei is a particularly important figure, acting as a protective older sister and mentor. The older, wiser agent Taisou serves as a father figure, while the burly Tetsugyu, who initially resents the danger that the boy’s importance attracts, eventually develops a deep fondness for him. However, his deepest bond is with Giant Robo itself. He does not view the robot merely as a weapon, but as a friend and, for a long time, his only true family. Their connection is profound and mutual; while Daisaku commands Robo with his voice, the machine is fiercely protective of its young master, and its auto-guard circuit can activate independently to save Daisaku if he is in peril.

In the main continuity of Giant Robo: The Night the Earth Stood Still, Daisaku’s role in the story is pivotal, as he is considered one of the IPO's most important operatives and a prime target for Big Fire. His development throughout the narrative centers on his struggle with the weight of his duty and his growing understanding of sacrifice and the complexities of justice. He begins as a boy who feels helpless and frustrated when separated from Giant Robo or forced to confront the limits of his power. Through harrowing battles, the sacrifices of his allies, and the gradual erosion of his simple ideals, he undergoes significant mental and emotional growth, learning to stand firm not just with his robot, but with his own resolve. He is forced to question what it means to be an adult and to find his own conviction in a world filled with moral ambiguity. His only notable ability is commanding Giant Robo via his wristwatch, but this singular power makes him one of the most significant figures in the global struggle between the Experts of Justice and the forces of Big Fire.