Senkou no Kishi ~Christia Knight~

During a deep space mining mission aboard the vessel Crouton, Aika discovers a planet inhabited by "lost emigrants"—humans who left Earth long ago. The planet grows Carystium, a substance outlawed by the Federation. Having lost her homeworld to the war over Carystium, Aika lands there to investigate. Meanwhile, Cerald, a native boy, trains to become a "Carystia Knight" to save his parents, stricken by a mysterious illness. A chance meeting binds them together on a journey to the Carystium-rich city of Krotovuria.