Soutarou Kobayashi, the accompanist of the legendary violin prodigy Ito Sakura, constantly feels inferior to him. But Ito only ever smiles and says, "Playing with Sou-kun is the most fun!" One day, the two suddenly find themselves lost in another world called Sonataria, where music possesses mysterious powers. In order to return to their original world, they set out on a journey to defeat monsters known as "Mythos" which threaten the world...