Sanshiro Tsuwabuki, known in some international versions as Brandon or Brando Drumond, is the central protagonist and main pilot of the giant super robot Gaiking. Before being thrust into an interstellar war, his life was defined by the world of professional sports. He was a rising star in Japanese baseball, a talented pitcher on the cusp of making his major league debut for the Red Sun team, where his exceptional abilities, including a signature Miracle Pitch, had generated tremendous expectations. This career was violently cut short when agents of the alien invasion force, the Dark Horror Army or Black Horror Army, staged an accident during a game that resulted in a severe fracture to his left wrist, an injury that forced his retirement from the sport he loved. This attack was not random; Tsuwabuki possessed latent psychic powers that made him a potential threat to the invasion plans of Emperor Darius, and the aliens sought to eliminate him without revealing their existence. After surviving further assassination attempts, he was recruited by the astrobiologist Professor Daimonji (also known as Dr. Diamond) to join the crew of the carrier superweapon Daiku Maryu and become the pilot of Gaiking.

Tsuwabuki's personality is marked by a compelling blend of fiery impulsiveness and deep sensitivity. Initially, he is described as brash, restless, and impulsive, a young man who does not easily adhere to strict instructions, which immediately puts him at odds with the more disciplined members of the Daiku Maryu's crew, such as the strict Pete. Despite his tough exterior and rebellious streak, he is also portrayed as a very sensitive and empathetic individual, capable of compassion even towards his enemies, a trait that sets him apart from a typical hardened warrior. His motivation evolves throughout the story. Initially, he is driven by a powerful desire for revenge against the alien Zelans who destroyed his baseball career and attempted to murder him. He experiences the loss of his former life traumatically, struggling to reconcile his will with the reality of his injury and his new, forced path as a soldier. However, this personal vendetta gradually transforms into a genuine sense of duty and responsibility as he accepts the monumental task of protecting Earth from conquest. Even as he dominates the battlefield, he never forgets his identity as a man with affections and desires for a peaceful life, a longing that only intensifies as the war steals his time.

Within the story's narrative, Tsuwabuki serves as the newest and arguably most crucial member of the eclectic Daiku Maryu crew, a team composed of other psychic misfits including an American navy pilot, a sumo wrestler, and a kickboxing champion. His primary role is the pilot of the titular super robot, Gaiking, a powerful mecha formed from parts of the carrier, distinguished by its skull-shaped golden torso and golden horns. His key relationship is with Professor Daimonji, the scientist who recognizes his latent powers and recruits him, giving him a new purpose. He also has a significant, conflict-driven relationship with Pete, whose strict nature clashes directly with Tsuwabuki's impulsive personality. The crew's dynamic is that of a found family of misfits, with Tsuwabuki being the hot-headed newcomer who must learn to work with others.

Tsuwabuki's development is central to the series. He transitions from a traumatized athlete seeking vengeance to a disciplined defender of humanity, learning to channel his natural valor and fighting spirit from baseball into piloting a giant robot. While his past never prepared him for fighting monsters, he rules on the battlefield with the same courage that could have made him a baseball champion. A key aspect of his character is his possession of super abilities and latent psychic powers, which are the very reason he was targeted by the Zelans and why he is uniquely qualified to pilot Gaiking, as he was one of the few remaining humans with sufficient psychic potential to operate the machine.