In Hoshi wo Ou Kodomo, Asuna Watase spends her days carrying responsibilities that leave little room for childhood, dividing her time between exceptional schoolwork and keeping her household running while her mother is away. Her only refuge is a hidden hideout in the mountains, where an old crystal radio gives her a brief escape from the pressure of always being needed. One day, the set catches a strange, melancholy melody unlike anything she has ever heard, and the sound feels like a call from beyond the world she knows.
Drawn onward by that song, Asuna meets an enigmatic boy named Shun, who saves her from a dangerous creature and leads her toward a long-lost land that seems to lie just beyond the edge of the familiar world. What begins as a quiet moment of listening turns into a journey through a hidden realm shaped by longing, memory, and wonder, where the life she once knew starts to feel like a distant echo. In that world, the melody becomes a guide, and Asuna must decide how far she is willing to go to follow it.