Saori Shiba is a young woman in her twenties who works as a reporter and photographer for the magazine Monthly Pro Tennis. She is often partnered with her senior colleague, the veteran reporter Mamoru Inoue. Shiba is a newcomer to the world of tennis journalism and initially has a poor grasp of the sport, leading her role to be focused more on taking photographs than on conducting interviews. In her early appearances, she is portrayed as slightly immature for her age and somewhat shallow, often showing a fascination with the appearance of the players she is assigned to cover. Despite this, she demonstrates a strong work ethic, such as when she announces her intention to personally cover all tennis-related events at Seishun Academy.

As the story progresses, Shiba matures both emotionally and professionally, gradually shedding her initial biases to become a more composed and capable journalist. She is known to be a fan of the prodigy Ryoma Echizen, though she is often put off by the behavior of his father, Nanjiro Echizen. A recurring trait of Shiba is her poor sense of direction, which sometimes leads to her getting lost while trying to reach tournament venues. Her professional journey includes making mistakes, such as accidentally publishing a photograph of Kaoru Kaido under Ryoma Echizen's name, but these experiences contribute to her growth in the field. She is frequently seen documenting the matches and practices of the Seigaku team, providing a journalist's perspective on the events surrounding the tennis circuit.

Kachiro Kato is a first-year student at Seishun Academy and a member of the school's tennis club, though he is not one of its regular starters. He is part of a close-knit group of friends that includes his classmates Satoshi Horio and Katsuo Mizuno, with whom he is often seen both in and out of practice, forming a trio known as the Freshman Trio. Kachiro is generally polite, meek, and somewhat timid by nature, which can make him appear vulnerable in the face of more intimidating characters. Despite this reserved demeanor, he possesses a strong sense of justice and has proven to be remarkably brave and stubborn when his beliefs are challenged, fighting tenaciously to defend what he thinks is right.

One of his primary roles in the story is as a loyal supporter and friend to Ryoma Echizen, the team's talented rookie. He shows his dedication by helping Ryoma, such as when he records matches of other players like Kaoru Kaido for Ryoma to study, even taking a hit to the eye in the process. Another significant display of his courage occurs when he challenges a bullying second-year player, Masashi Arai, who had spoken ill of the team's regulars. Despite being completely outmatched in skill and facing the consequence of having to quit the club if he lost, Kachiro persists in the match and gradually begins to return Arai's shots. The match is stopped, and Kachiro later gains respect for Arai upon learning that he had been playing with ankle weights. Kachiro is right-handed and, while not a standout player in terms of ability, his value lies in his unwavering team spirit, his loyalty as a friend, and his willingness to act as support staff, such as by gathering information on opponents. His father works as a coach at a tennis club and was unable to become a professional player due to an injury, a fact that has been a source of harassment from others in the past.