Rin Himesato is a shy, normal girl who worries that her tits are a little bigger than everyone else. One day, on her way home, Rin is attacked by Hamelder, an evil organization that has infested the city. She is in a desperate situation. The one who saves her then is a friend of justice and a student in the last year of the school, Sumire Hiyama, known as Frostia, the Magical Princess of Fighting.