In the future, mankind will venture to the far reaches of the cosmos using technologically advanced trains. The fleet of the Galaxy Railways transports countless galactic citizens from one exotic planet to the next, protected by the Space Defence Force, or SDF, the elite force protecting the Railways Fleet against terrorists, meteor storms and malicious alien life.
In the beginning of the story, the main character, Manabu Yūki, has always had dreams of joining the SDF, following in the footsteps of his father and brother, who died while serving in the SDF. Unfortunately, his mother is fed up with losing her family to the great space beyond and does what she can to deter him from following his dream. Despite this, Manabu is determined to join, and boards the train to Destiny Station, the story leads on from there.