To save her younger sister Aria from her illness, Cassmire Crisis became a mercenary, wielding a sword and shedding blood to pay for her medicine. But when Cassmire suffers a fall one day, memories of her past life as Aria’s wicked stepsister come flooding back. Rather than take up the role of villainess again, Cassmire vows to protect Aria this time. But with Aria doomed by the story to face only hardships, Cassmire must pick up her weapon once more to become her sister’s loyal sword!