Jimi Hime to Kuroneko no, Enman na Konyaku Haki

Are sweets and cats the key to peacefully calling off an engagement?!

Seren, the eldest daughter of a duke, has grown up being teased for her plain looks, nicknamed "Princess Drab" in comparison to her younger sister, who is a real beauty. One day she overhears her fiancé, Prince Helios, and his friends talking about how her sister would make a much better wife.

In order to avoid marriage with the prince, Seren plans to become a top-level magician and gain the freedom that comes with the title. To achieve this, she teams up with a black cat, a familiar lent to her by Viol, leader of the Ice Magicians, after she finds out about his secret weakness to sweets! Together they're going to do whatever it takes to bring a peaceful end to her unwanted engagement!

(Source: Cross Infinite World)