A fictional disaster has struck our Earth. Monsters suddenly appeared in the 119th year of the Old Euro Calendar. They were created based on Catastromechs. Scarlet Girls is a game about the journey of female heroes trying to save human civilization from the brink of collapse. The price for these warriors is transformation. To gain power, scientists have combined these girls with the energy core of Catastromechs. These girls are called Stellar Spirits. The battle will be extremely fierce. With power shared from the same source, the two forces will try to destroy each other to gain control. Can you win? Or will your world fall into a dark era where humans are just slaves?