My Dear Grand Duke on a Leash

Seduce the first man you meet within a week and get married…?
Before her sister’s wedding, Lariette was unexpectedly proposed to by Prince Narkissis of the Helios Empire to marry his cousin, Grand Duke Cain Acheron, for a one-year contract and be a spy. When Narkissis threatened her sister’s life, Lariette had no choice but to seduce Cain, but her attempt bounced off his otherworldly iron walls.
In the process, Cain reveals the secret of his family to her, and the two of them enter into a contractual marriage without any recourse.
Cain would keep her and her family safe, and Lariette would give birth to his heir.
The marriage scandal broke out as the two acted with lascivious fire in their eyes, but Lariette was confused.
“I came early because I wanted to see the princess as soon as possible.”
…Is this really acting?
His personality suddenly changed entirely… as if he had wanted her from the beginning!