The Precious Sister of the Villainous Grand Duke

Story:

I was reborn in a novel where my brother is a villain who loves blood and destruction. Growing up in a brutal family that forces children to fight for heirs … I decided to stay close to my brother in order to survive! I need you to be my guardian until I get out of here. I just have to wait and play little sister until the righteous and holy knight comes to punish this villainous brother.