"Gekijō-ban Hibike! Euphonium: Kitauji Kōkō Suisōgaku-Bu e Yōkoso" is a film adaptation that serves as a recap and expansion of the first season of the "Hibike! Euphonium" anime series. The story centers on Kumiko Oumae, a high school student who joins the concert band at Kitauji High School after a lackluster experience in her middle school band. Initially hesitant due to past disappointments, Kumiko gradually rekindles her passion for music as she becomes immersed in the band's rigorous preparations for the national competition.

The narrative explores the dynamics within the Kitauji High School Concert Band, highlighting the challenges of teamwork, personal growth, and the pursuit of excellence. Kumiko, who plays the euphonium, forms connections with her fellow band members, including her childhood friend Shuuichi Tsukamoto, the determined trumpet player Reina Kousaka, and the strict but dedicated band advisor Noboru Taki. The film delves into the band's struggles to overcome internal conflicts, such as differing levels of commitment and the pressure to perform at a high level, while also addressing individual characters' personal journeys.

Key plot points include the band's efforts to improve their skills, the selection process for competition spots, and the emotional highs and lows of striving for a shared goal. The story emphasizes themes of perseverance, self-discovery, and the transformative power of music, as the characters navigate their relationships and aspirations. The film condenses the first season's events while adding new scenes and perspectives, offering a cohesive and engaging retelling of the band's journey toward the national stage.