"Lost Song" is a 12-episode anime series that intertwines fantasy, music, and drama, centering on the power of song and its impact on the world. The story is set in a medieval-inspired fantasy realm where songs hold magical properties, capable of healing, summoning rain, or even causing destruction. The narrative unfolds through the perspectives of two primary characters: Rin, a cheerful and optimistic village girl with a hidden talent for singing, and Finis, a reserved and melancholic noble girl who also possesses the ability to wield song magic.

Rin lives a simple life in a remote village, unaware of the full extent of her abilities. Her life changes when she meets a traveling bard named Al, who recognizes her potential and encourages her to explore her gift. Meanwhile, Finis, who resides in a grand castle, is burdened by her role as a songstress and the expectations placed upon her by her family and society. Her songs are used to maintain peace and prosperity, but she struggles with feelings of isolation and the weight of her responsibilities.

As the story progresses, the two girls’ paths converge, revealing a deeper connection between them. Rin’s journey leads her to discover the true nature of song magic and its potential for both creation and destruction. Finis, on the other hand, grapples with her own identity and the moral implications of using her powers for political and military purposes. The narrative explores themes of friendship, sacrifice, and the consequences of wielding great power, as Rin and Finis navigate their roles in a world where songs can shape reality.

The plot takes a dramatic turn when it is revealed that the two girls are linked by a shared destiny tied to an ancient legend. This legend speaks of a lost song capable of altering the fate of the world, and both Rin and Finis become central figures in the struggle to either preserve or destroy this power. The series balances moments of lightheartedness and emotional depth, culminating in a resolution that underscores the transformative power of music and the strength of human connection.

The supporting cast includes characters such as Henry, a knight loyal to Finis, and Curtis, a soldier with a mysterious past, both of whom play significant roles in the unfolding events. The world-building incorporates elements of fantasy and mythology, with a focus on the cultural significance of song magic and its influence on the political and social structures of the world. "Lost Song" presents a narrative that blends personal growth, magical intrigue, and the enduring impact of music on the human spirit.