My Dog-like Grand Duke

"You want me to seduce a man I just met and marry him in a week?" Ahead of her sister’s wedding, Riette, the Princess of Chalone, meets the Imperial Prince who has arrived as a celebratory envoy. But instead of a gift, this Prince delivers a threat. "Marry my cousin, Kain, and dig up his weakness." "If a princess about to be married were to pass away... wouldn't that be a tragedy?" To protect her sister, Riette attempts to seduce Kain—the "Iron Grand Duke," a man so cold he is called an ice pick and a human machine—but she hits a wall from the very start. "Please refrain from approaching me." Kain ruthlessly deflects all of Riette's efforts. Eventually, Riette even proposes a contract marriage to become his wife, but... "You seemed to have a hard time last night, so I will be gentle today." The image of Kain as an impenetrable iron fortress is nowhere to be found. Why has he started clinging to Riette like a puppy...?