Aoi Kentarou is a first-year student and the captain of the Rokkaku Middle School tennis club, an unusual position given his age as he was appointed directly by the team's coach. He was born on December 20th, making his zodiac sign Sagittarius, and has O blood type. Standing at 165 centimeters tall and weighing approximately 53 kilograms, Aoi has a distinctive appearance characterized by his shaved head and slender build. His family consists of his grandparents, parents, and two older brothers, with his father working for a construction company.

Aoi is known for his cheerful, energetic, and talkative personality. He is described as a very friendly individual who tries to make friends with everyone he meets. His loud voice is one of his most noticeable traits. As a typical adolescent boy, he is keenly interested in becoming popular with girls and frequently daydreams about finding a cute girlfriend, though he is said to have a one hundred percent rejection rate. Despite his sometimes simple-minded and overconfident demeanor, he possesses strong endurance and is diligent about his practice, never skipping warm-up exercises before matches. His teammates note that he does not plan things out in advance but is never boring to be around.

Aoi's motivation for playing tennis is closely tied to his desire to be popular with girls. His unique approach to competition involves deliberately putting himself under extreme pressure to unlock his true potential. He typically allows his opponents to win the first several games, creating a deficit for himself, and then uses romantic self-motivation such as telling himself that he will never be popular if he cannot make a comeback. This strategy, born from his strong mental fortitude and youthful confidence, had been successful throughout prefectural tournaments before he faced national-level competition.

Within the story, Aoi serves as the captain of Rokkaku Middle School, leading his team through the Kanto Tournament and the National Tournament. He is a regular singles player, typically competing in the third singles position. His most significant matches include facing Kaidoh Kaoru in the manga version of the Kanto Tournament semifinals, where he lost after tying the score at four games each, and facing Echizen Ryoma in the anime adaptation of the same match, which he also lost. At the National Tournament, he suffered a decisive loss against Chinen Hiroshi of Higa Middle School, failing to win a single game.

Aoi has meaningful relationships with his teammates at Rokkoku. He looks up to his upperclassman Saeki Kojiro, though he also envies Saeki's success with girls. His teammate Kurobane Harukaze acknowledges his unique abilities, noting that he excels at playing under pressure as well as unconventional competitions like clam hunting and underwater breath-holding. The coach who appointed him captain, known as Ojii, created a special hexagonal racket for him where the entire string bed functions as a sweet spot, enhancing his control and allowing him to turn every return into an offensive shot.

Aoi's notable abilities revolve around his exceptional ball control. His signature technique is the Cord Ball, a shot that deliberately hits the top of the net cord and drops into the opponent's court. His precision is so refined that he can aim for and hit the net cord at will. He plays as an aggressive baseliner, using his right hand as his dominant arm. His training under Ojii combined with his custom racket allows him to consistently hit to the same spot on the opponent's side regardless of placement, frustrating his opponents. Beyond tennis, he has perfect vision of 2.0 in both eyes, serves as the broadcasting committee member for his school, and enjoys activities such as playing at the beach and assembling plastic models.