Seduce a man you just met within a week and marry him?

Ahead of her sister's wedding, Princess Liet of Shamrone meets the Empire's Prince, who arrived as a congratulatory envoy. But this Prince, far from offering gifts, delivers a threat.

"Marry my cousin, Kain, and dig up his weaknesses."
"If a princess about to be married passes away... wouldn't that be a tragedy?"

To protect her sister, Liet tries to seduce Kain, the Grand Duke of Iron, known as a cyborg and as cold as an ice fortress, but she hits a wall from the very beginning.

"Please refrain from approaching me."

Kain unhesitatingly rejected all of Liet's efforts. In the end, Liet even proposes a contract marriage, trying to become his wife...

"You seemed quite tired last night, so I will be gentle today."

Kain, who was like an impregnable fortress, is nowhere to be found, and instead starts clinging to Liet like a dog...?