Narikin Shouka Monogatari: Tsundere Oji-san wa Bijin na Toshishita Josei wo Iyaiya Metoru

Jeweler Alfonso's fourth wife, Mercedes, is a beautiful woman with the unusual background of being a former knight. However, having had an unfortunate upbringing and been divorced three times, he distrusts women and shows no signs of being a newlywed. Mercedes, on the other hand, diligently fulfills her role as mistress of the house, but is troubled by her husband's inscrutable emotional fluctuations and his reluctance to open up. "Every couple overcomes trials before they can become a family"—a revelation Mercedes receives, and begins her search for what it truly means to be a "real couple"…

(Source: Futami Shobo, translated)