Joe Kaisaka is the main protagonist and primary pilot of the giant robot Groizer X. He is a young man residing on Akane Island, where he is a student at a hero academy. Out of all the people at this academy, he is distinguished as the most skilled pilot of flying aircraft. His life changes dramatically when he encounters Rita, a wounded alien who has escaped from the clutches of the Gaira invaders with the ultimate weapon, the transforming robot Groizer X. After meeting her, Joe takes control of the robot, becoming its main pilot and Earth's primary defender against the extraterrestrial threat.

In terms of personality, Joe is fundamentally a heroic and selfless individual. He is characterized as a nice guy who has no hesitation in helping complete strangers without expecting anything in return. However, this heroic nature is paired with a more rough-edged temperament. He is initially presented as a competitive and somewhat aggressive person who has difficulty relating to others due to his hot-headed and difficult disposition. Despite this initial roughness, a core part of his personality is his deep-seated kindness, especially towards children. Having grown up as an orphan himself, he understands the pain of loneliness and shows great warmth and compassion to young people wherever he goes, earning their adoration in return. This combination of a gruff exterior and a caring heart makes him a complex hero.

Joe's motivations are driven by a powerful sense of justice and a desire to protect his adopted home. His decision to pilot Groizer X is a direct response to the threat posed by the Gaira aliens, choosing to fight for Earth's safety. His role in the story is that of the champion of Earth, using the Groizer X to battle the giant monsters and robots sent by the alien emperor Geldon. He serves as the courageous and capable field commander in the fight against the invasion, with Rita acting as his second-in-command.

The most important relationships in Joe's life inform his character greatly. His relationship with Professor Tobishima is central to his background. After the death of his parents, Joe was happily adopted by the professor, who serves as a gentle yet strict father figure and mentor to him. Joe adores the professor completely, and the professor is his great friend and advisor. His relationship with his friend and fellow student Sabu is that of a cool big brother, always looking out for him when he gets into mischief. His most pivotal relationship, however, is with Rita, the alien girl who brought the robot to Earth. They share a deep and tragic romance as star-crossed lovers, as their respective home worlds are at war with each other. Although they fight side-by-side and care for each other deeply, the circumstances of the conflict prevent them from becoming a permanent couple in the end.

Joe Kaisaka undergoes a notable character development over the course of the series. While he begins as a competitive and somewhat quarrelsome young man with a violent temper, his experiences piloting Groizer X and his deepening relationship with Rita help him to modify his behavior. He gradually evolves from a hot-headed rival into a generous, reliable, and accessible hero. As a pilot, Joe possesses exceptional abilities. He is recognized as an ace pilot, showcasing unmatched skill in aerial combat. His most notable ability, however, is his expert piloting of the giant Groizer X, which he uses to perform incredible feats in the battle to save the planet.