I Raised My Younger Sister Beautifully

The imperial family collapsed in one night. By Basilisk, the summoner of darkness; summoned by Fletta, the Cursed Princess.
“If there is a next life… Can I really be your sister?”
Would it have been different if I had approached you a little more?
It was the last time everyone regretted it, and like a miracle, time returned to six years ago. If this is the second chance given to us…
‘Yes, I’ll heal you. To prevent the awakening of the Basilisk’s darkness.’
So I decided.
“I look forward to your kind cooperation, Grand Duke Darian. No, Kylia.”
I decided to marry Fletta’s maternal uncle, Grand Duke Kylia.
I thought there would be no problem because it was a one-year contract marriage.
“Honey, ah, try it.”
“You have no idea how much I like you.”
“I will continue to like you. I want to express my affection to my heart’s content… Can’t I?”
What’s wrong with this guy?
When I try to save Fletta, the Grand Duke comes along with me (?)
Aren’t you the Monster Grand Duke…?