The Princess's Vampire-Raising Diary

On a continent in the northwest of the world, a princess defies her father's orders and ignores the judgment of others. She insists on rescuing her younger sister, who has lived in darkness for four years, and flees the royal city with her. They meet a red-thread immortal, a pair of vampires, and a blond demon who claims to be the progenitor of vampires and wants to take her sister away.

Many years later...

"Sister, you know? I like you so, so much now." Bianca lowered her head, her loving eyes fixed on the person resting on her lap.

"Bianca, what did you just say?"

"Ah~ Sister, what are you talking about? I don't know anything, meow~"