Hikaru Sato is the son of Toshiya Sato, who was a famous home run king in the major leagues and the longtime best friend and rival of Goro Shigeno, the protagonist of the original series. Hikaru lived in the United States before moving back to Japan, which has given him fluency in English. When he first appears, he approaches other children looking specifically for the son of Goro Shigeno, expressing a strong interest in meeting him.

Unlike the protagonist Daigo Shigeno, who struggles with a lack of natural baseball talent, Hikaru possesses exceptional physical abilities and a very strong throwing arm. His pitching style is aggressive and power-based, reminiscent of Goro Shigeno rather than his own father, who was a catcher known for his intelligence. Despite his famous parentage, Hikaru is initially inexperienced and knows very little about the sport of baseball, as his father encouraged him to try other activities. Once shown the fundamentals, however, he masters new skills with remarkable speed.

Hikaru has a calm and cheerful personality that sometimes comes across as arrogant due to his overflowing confidence. He is a new transfer student in Daigo's class, and his looks are often talked about by the girls at school. He has very poor eyesight and must wear glasses. When he first starts playing, he mixes English words into his speech.

His initial motivation for playing baseball is not a deep love for the sport. He finds the game boring because players in the field do not get to touch the ball every play. His passion is ignited more by the challenge of playing with and against Daigo Shigeno, whose deep knowledge and love for baseball he recognizes and respects. He proposes to Daigo that they form a pitcher-catcher battery, a promise that becomes the central driving force for both characters. Hikaru quickly decides he wants to be a pitcher, which he calls the flower of baseball, contrasting with his father Toshiya who was a legendary catcher.

Hikaru's role in the story is as both a teammate and a rival to Daigo. After joining the Mifune Dolphins, he forms a formidable battery with Daigo as his catcher and helps lead the team through tournaments. A significant turning point occurs when Hikaru suffers a severe neck injury from a collision during a game. Daigo blames himself for this accident, which creates a deep emotional wound between them. Following this event, Hikaru's family moves away, and he disappears from the main narrative for a long period.

During his absence, Hikaru undergoes a significant personal and athletic transformation. He endures a painful rehabilitation to recover from his injury, which initially threatened to paralyze him. He later transfers to a different school, Tsujido, where he makes the varsity baseball team. When he reappears, he has changed his surname to his mother's, Sakaguchi, and due to his injury, he can no longer pitch. He has instead converted to being a catcher, a position his father once held. His personality also seems to have hardened; he is driven by a powerful need to get back on the field and appears cold and brutally honest towards Daigo, whom he feels has not lived up to their childhood promise. Despite these changes, he demonstrates excellent batting ability, including hitting a home run in his first game back.

Hikaru's notable abilities include a natural talent for baseball that allows him to learn and execute skills almost immediately after being taught. He is a powerful hitter and, before his injury, was a dominant pitcher who relied on a strong fastball. After transitioning to catcher, he shows excellent game sense and leadership, quickly bringing an unruly pitcher under control. His athleticism and instincts on the field continue to make him a standout player despite his changed circumstances.