Ichinichi Ichi Jikan Dake Neko ni Naru Imouto

Mayanna, the daughter of a marquis, comes from a family renowned for magic, but is a failure who can only use outdated rune magic. What's more, she is overworked by her older sister, a talented magician, and even has her fiance taken away from her, making her a pitiful victim. Then, one day, Prince Alectos, a great genius in magic, comes to visit Mayanna... "Mayanna Pheles... I've come to scout you." Will outdated rune magic save the country?! The reversal of Mayanna's life, once scorned as her older sister's waste, begins now!

(Source: Futabasha, translated)