I Hid The Crazy Grand Duke’s Time-limited Younger Brother

I found myself transmigrated into a novel full of obsession and tragedy, but I didn’t care one bit. I was neither the heroine nor the villainess; I was just a passing noblewoman. I felt a bit of remorse for the heroine, who would rescue a child and suffer at the hands of the villain, but the male lead would save her in the end, anyway.
I had nothing to worry about in my life.
“This is insane! Are you crazy, Brother?!”
Until my lunatic older brother came to me and said, “I have a gift for you!” and brought THAT child!
“Doesn’t he resemble that stray cat you used to like when you were little?”
Whatever! Take him back right now!
* * *
‘It’s fine, as long as I don’t get caught…’
I pretended to help the villain, who was madly looking for his missing younger brother, while I secretly kept an eye on him.
I was determined not to hand the child over to a human who wanted to use his little brother as a pawn in war, but…
“Rayna, tell me.”
His grip on my ankle grew stronger.
“Why do you keep lying to me and hiding Calyx, my little brother?”