While on a deep space exploration mission aboard the mining vessel Crouton, Aika discovered a planet of "lost emigrants" who had long ago departed from Earth.
The planet was growing Carystium, which was against federal regulations.
Having lost her homeworld over Carystium, Aika landed on this free world to explore.

Meanwhile, Cerald of this free world was training to become a "Carystia Knight" for the sake of parents stricken by a strange illness.
Cerald and Aika met by chance, they joined hands in the journey to the Carystium-rich city of Krotovuria.

[From DLsite English]