The stage is the Gurhal Star System, which consists of three planets. Each planet has its own unique culture that is formed by its inhabitant races.

The history of the Gurhal Star System is filled with conflicts amongst the different races. However, after the Final Conflict 100 years ago, a union was formed amongst the three planets. The led to the birth to the Allied Army, and ultimately to peace for the Gurhal Star System.

At the start of the game, Ethan, the main character, and his little sister Lumia, were at the celebration of the 100th year anniversary of the Alliance Space Fleet on the GUARDIANS Space station. The celebration is ended when a mysterious meteor shower almost destroys the entire fleet. During evacuation, Ethan and Lumia split off of the main evacuation route, and A pile of rubble separates Lumia from Ethan. Ethan then meets up with a GUARDIAN named Leo, but they are attacked by some sort of creature. The creature paralyzes Leo, and Ethan takes his handgun and kills the creature. Leo then tells Ethan to find his sister, and that a rescue team is on the way.

After killing multiple creatures and saving people, Ethan Finds Lumia, and they both leave the station, but after a conversation between Leo and Ethan, revealing that he dislikes GUARDIANS because his father died when on a mission. He then convinces Ethan to join the GUARDIANS.

After Ethan's training, he joins up with his training partners, and performs various missions, such as rescue, purification, and escort missions.