Plot
The series take place in the future, after mankind migrated to the planet Mars, home to the Martians. Before long, the humans begin persecuting the Martians, and the two species form a mutual hatred of each other.
The action takes place Heden City, a frontier town and home to the Hoshino family. One day, Ken Minakami comes from Earth to visit her relatives, the Hoshino family. Not long after she arrives, a mysterious gunman calling himself "Captain Ken" appears in Heden City. Captain Ken is a human fights on the side of the Martians, protecting them from those who wish to exploit them for their own gain.
Mamoru Hoshino, the eldest son of the Hoshino family, begins to suspect that Ken Minakami may be the mysterious gunslinger, Captain Ken.