"Adesugata Mahou no Sannin Musume" centers on three young girls—Rin, Suzu, and Kotone—who are students at a magical academy where they learn to harness their unique abilities. Rin, the protagonist, is a diligent and determined girl with a strong sense of justice, though she often struggles with self-doubt. Suzu, her best friend, is cheerful and optimistic, providing emotional support to Rin while excelling in healing magic. Kotone, the third member of their trio, is reserved and analytical, often acting as the strategist of the group. Together, they navigate the challenges of their magical education while forming a close bond.

The story begins with the trio entering their second year at the academy, where they are introduced to more advanced magical techniques and responsibilities. Their studies are interrupted when a mysterious force begins disrupting the balance of magic in their world, causing anomalies and endangering both the academy and the surrounding regions. The girls are drawn into the conflict when they discover that the disturbances are linked to an ancient artifact, the "Eclipse Shard," which has the power to amplify or destabilize magical energy.

As they investigate the artifact, Rin, Suzu, and Kotone uncover a hidden history involving their academy and a long-forgotten magical war. They learn that the Eclipse Shard was created as a weapon during this war, and its resurgence threatens to reignite old conflicts. The girls must confront their own insecurities and fears while working together to prevent the artifact from falling into the wrong hands. Along the way, they encounter allies and adversaries, including former students and powerful magical entities, each with their own motivations and connections to the artifact.

The narrative explores themes of friendship, perseverance, and the ethical use of power, as the trio grapples with the consequences of their actions and the responsibilities that come with their abilities. The story balances moments of lighthearted camaraderie with intense magical battles and emotional growth, culminating in a climactic confrontation that tests their resolve and unity. Through their journey, Rin, Suzu, and Kotone not only grow as magicians but also as individuals, learning to trust in themselves and each other.