The Precious Sister of the Villainous Grand Duke

I became the sister of the villain, who shed no blood or tears in a war-ridden novel! I thought I was born again as the youngest daughter of a noble family, but I'm the little sister of a villain who's only being used! A baby's body too fragile to survive in the Lagrange household, a brutal family that makes children fight for successors… I've decided to stick to the villain in order to live! I need you to be my guardian until I run away from here. Raise me, villain! ---