Hiroki Takasugi is the son of a wealthy family and is one of the most popular and talented star players on the Kisaragi Boys' High School baseball team. He is a handsome and charismatic figure, possessing blue or green eyes and blonde hair. Because of his family's social standing and his own athletic success, he was initially being groomed as a potential boyfriend or fiancé for Izumi Himuro, the daughter of the school's president.

In terms of personality, Hiroki is known for being incredibly kind and supportive, always willing to help others regardless of any inconvenience to himself. He exhibits a playful and teasing side, most notably in his persistent habit of calling the protagonist Ryo Hayakawa by an affectionate nickname, Ganmo-chan or Tofu-girl, which is a reference to her family's oden restaurant. While he is generally supportive and enjoys seeing others succeed, he is also very competitive in spirit and known for being to-the-point and direct when he feels strongly about someone or something. His sincerity and lack of self-absorption set him apart from the typical "pretty boy" archetype.

Hiroki's primary motivation throughout the story is intrinsically linked to his growing feelings for Ryo Hayakawa. From the moment he encounters her, he feels an instant attraction, to the point where he goes out of his way to nickname her and engage with her. His interest in Ryo becomes a central driving force, complicating the pre-existing dynamic between Ryo and Izumi, as he seizes the opportunity to be near and support Ryo's fledgling baseball team. He is driven by a genuine care for Ryo's well-being and success, as well as the competitive challenge of facing her on the baseball field.

In the story, Hiroki serves as a major catalyst for the central love triangle and as a key rival on the baseball diamond. His status as a top hitter makes him a formidable opponent. This rivalry reaches its peak when the Kisaragi girls' team faces the boys' team in the tournament semifinals, turning the game into a personal duel between Hiroki and Ryo, intensified by their mutual attraction. Off the field, his family's wealth and connections, particularly through his grandfather, play a role in the unfolding drama surrounding the scandal involving Ryo's late father.

His key relationships are with Ryo Hayakawa and Izumi Himuro. He initially sees Izumi as nothing more than a sister, which creates tension as Izumi's feelings for him are more complex and fueled by her rivalry with Ryo. His relationship with Ryo evolves from playful teasing to a deep romantic connection, though he struggles to openly profess his love until the series' climax. He is also a supportive figure to both girls, coaching them and offering emotional support during difficult times.

Hiroki undergoes subtle but important development from a talented but somewhat passive heartthrob to a young man who actively takes a stand. In the series finale, he finally professes his love for Ryo, moving beyond his previously indecisive position in the love triangle. His final confrontation with Ryo in the semifinal game results in a game-winning home run, demonstrating that when his competitive spirit is at its peak, he is willing to directly challenge the person he cares about most.

Regarding his notable abilities, Hiroki is an elite baseball player, specifically recognized as a genius slugger and top hitter for the Kisaragi boys' team. His athletic skill is on par with Ryo's pitching prowess, making their duels the central sporting events of the series.