"Gekijōban Mahōka Kōkō no Rettōsei: Hoshi o Yobu Shōjo" is a manga adaptation of the light novel series "Mahōka Kōkō no Rettōsei," focusing on a self-contained story set within its universe. The narrative centers on Tatsuya Shiba, a technically inept magician with exceptional combat skills, and his sister Miyuki, a prodigious magician. The story unfolds during their time at First High School, a prestigious institution for training magicians in a world where magic is systematized through modern technology.

The plot revolves around a mysterious incident involving a powerful ancient magical artifact known as the "Relic." This artifact, capable of summoning a catastrophic event tied to the stars, becomes the focal point of a conflict between various factions. Tatsuya and Miyuki are drawn into the investigation when their schoolmates and friends are implicated in the artifact's activation. As the situation escalates, the siblings must navigate a web of political intrigue, rivalries, and hidden agendas to prevent the Relic from unleashing destruction.

Key characters include Tatsuya, whose unique abilities and strategic mind make him a formidable force despite his technical limitations, and Miyuki, whose immense magical prowess and loyalty to her brother play a crucial role in their efforts. Supporting characters such as Erika Chiba, Leonhard Saijo, and Mizuki Shibata contribute to the dynamic, each bringing their own skills and perspectives to the unfolding crisis. The story also introduces new characters specific to this arc, including antagonists who seek to exploit the Relic for their own purposes.

The manga explores themes of power, responsibility, and the ethical implications of advanced magic, set against a backdrop of high-stakes action and intricate world-building. The narrative maintains a balance between character-driven moments and larger-scale conflicts, providing a cohesive and engaging experience within the established "Mahōka Kōkō no Rettōsei" universe.