My Sister Picked up the Male Lead

My name is Amy. I'm glad to have been reborn as the main character's little sister in a novel from my past life but... On the morning I turned sixteen, my sister said she prepared something special for me and had picked up a man from the woods?!! It's shocking enough that my sister picked up a strange man, but even more shocking is that he is Lennox Iberich, a child of royal blood with a curse that transforms him into an adult man at nighttime, and also the main character of the story! “Who are you?” “T-The one that brought you here is me!” In the novel, my sister who picked up the male lead is fated to die, so instead, I've taken the target for that cause... “Amy. I can only see you at night, and a night without you... is meaningless.”