Yuu Maxwell's life was pretty normal at first with her foster sister Riku Maxwell until parents were killed from assassin who was after Yuu. Yuu and Riku manged to escape and meet a girl named Mei Himura, a person who works under Knight of Atlus to stop a threat lurking in the shadow, Yuu helped Mei with her mission; little did Yuu knowns that her life will change forever.