Hanayome Shugyou wo Yametakute, Reitetsu Koushaku no 13-banme no Konyakusha ni Narimasu

Ilaria, the daughter of a fallen nobleman, is forced to undergo rigorous training to marry a man of high status in order to restore her family's fortunes. At a ball where she is looking to meet someone, Elliot, who is rumored to be a "cold-hearted duke" who has broken off 12 engagements, suddenly asks her to marry him, and they end up living together in a mansion...? A duke with a history and a down-on-her-luck noble daughter with a good heart!

(Source: COMICSMART, translated)