Eren Yeager's Wife's Manga

Delma and Louise were born as twin daughters of the famous Praetoria family, but needing a son to inherit the position as marquis, Del is raised as a man by her mother whilst neglecting the other twin. As she endures the position as heir, their mother plans to get rid of her and establish a real man as the marquis, through her sister’s arranged marriage but not before a dragon, an ancient being, appeared before them with a contract as salvation...