Zettai Ni Kekkon Shitakunai Reijo, Henkyo No Kedamono To Yobareru Shogun Kakka No Oshikake Tsuma Ni Naru

Due to certain circumstances, Francesca is to marry Matthias, a strict soldier known as the "Beast of the Frontier." Matthias is older and misanthropic, but he doesn't trust her and proposes a chaste marriage... but she doesn't give up at all. As Francesca works hard as the lord's wife, her heart begins to melt... A love comedy about two people who harbor secrets they can't tell each other!

(Source: Comic Walker, translated)