"Hi Score Girl" is set in the early 1990s and centers on Haruo Yaguchi, a sixth-grade boy whose life revolves around arcade gaming. Haruo prides himself on his skills, particularly in Street Fighter II, and spends most of his time at local arcades. His world is disrupted when Akira Oono, a quiet and wealthy classmate, unexpectedly defeats him in a game. Despite her reserved demeanor, Akira is a formidable gamer, and her victories challenge Haruo's self-perception as the best. Their rivalry evolves into an unlikely friendship, with gaming serving as the foundation of their bond.

As the story progresses, Haruo and Akira navigate the complexities of adolescence, school life, and their growing feelings for each other. Their relationship is complicated by Akira's strict upbringing and her family's expectations, which often limit her freedom. The narrative also introduces Koharu Hidaka, a cheerful and energetic girl who becomes Haruo's friend and develops feelings for him. Koharu's presence adds a layer of romantic tension, as she competes with Akira for Haruo's attention, though Haruo remains largely oblivious to their affections.

The series explores themes of friendship, rivalry, and first love, all set against the backdrop of the 1990s arcade gaming culture. The story captures the nostalgia of the era, with frequent references to classic games and the evolving gaming industry. Haruo's passion for gaming serves as both a source of joy and a means of escape, while his interactions with Akira and Koharu highlight the challenges of communication and emotional vulnerability.

Throughout the series, the characters face personal growth and confront their insecurities. Haruo learns to appreciate the value of relationships beyond gaming, while Akira struggles to assert her independence. Koharu, despite her unrequited feelings, remains a supportive friend, embodying resilience and optimism. The narrative balances humor, heartfelt moments, and the competitive spirit of gaming, creating a story that resonates with both gaming enthusiasts and those interested in character-driven dramas.