Jimi Dasa Reijou ga Koushaku-sama wo Futta no ni, Naze ka Shitei Kankei ni Narimashita. Chouai Sarete mo Kokoro wa Kawarimasen!

Siena is courted by the Duke of Highlander, the king's younger brother, who is famous for his good looks! She refuses, saying she has no intention of ever marrying, but there's a secret behind her decision. Siena's family has prospered thanks to magic, and the sorcerer who cast that spell has died! If things continue like this, her family may fall into ruin. Prioritizing her family over marriage, she tries to do something about it by apprenticing at a renowned magic academy... but the sorcerer there looks just like the Duke of Highlander...!? (Source: Kodansha, translated)